CHAPTER ONE INTRODUCTION Background to the

CHAPTER ONE INTRODUCTION Background to the Study Joint disease affects a lot of people throughout the world, causing pain and disability with great impact on individuals and society as a whole. Osteoarthritis (OA), the most common joint disease, is projected in the near future to rank second for women and fourth for men in developed countries in terms of years lived with disability. Osteoarthritis is a degenerative condition affecting synovial joints, and it is the most common condition affecting people aged 40 years and above. In 2004, one hundred and fifty one million people worldwide experienced OA which was ranked sixth as a leading cause of moderate and severe disability (World Health Organization, 2008). It is generally defined as a slowly progressive monoarticular disorder of obscure aetiology (Symmons, Mathers and Pfleger, 2006). The condition occurs late in life, principally affecting the hands and large weight-bearing joints, and is characterized by pain, deformity, enlargement of the joints and limitation of motion. Though the specific causes of OA are unknown. It is believed to be a result of both mechanical and molecular events in the affected joint. The disease onset is gradual and usually begins after the age of 40 with painless changes in components of the joint cartilage such as collagen and the substances that provide the cartilage's resilience (proteoglycans). As the cartilage starts to erode, particles irritate the joint lining (synovium) causing stiffness, inflammation, and swelling (CDC, 2009). The knee, one of the largest and most complex synovial joints in the body, is one of the most commonly affected joints. It provides the body with stable support and also allows the legs to bend and straighten. The knee is more predisposed to injury than any other joint in the body and is more likely to be ignored because of its seemingly strong appearance until something that causes pain happens to it. The joint also has a structure made of cartilage, which is called the meniscus or meniscal cartilage. It helps to protect the joint surface and allows the bones to slide freely on each other. There is no doubt that OA occurs all over the world, although ethnic differences in its prevalence exist (Mody and Woolf, 2003). Knee OA is one of the five leading causes of disability among non-institutionalised adults in United State, occurring in 10% men and 13% women aged 60years and above (Zhang and Jordan, 2010). In United Kingdom primary care, older adult’s knee pain is a common disabling problem with OA as the most likely underlying diagnosis (Foster, Thomas, Barlas, Hill, Young, Mason and Hay, 2007). 1

Knee OA is more prevalent in rural area of Iran than other Asian countries (Arash, Fereydoun, Ahmad-Reza, Tahereh, Pedram and Mozhgan, 2014). Many hospital-based studies have shown that OA is common in Nigeria (Akinpelu, Alonge, Adekanla and Odole, 2007). Two hundred and five (119 females and 86 males) aged forty years and above, out of one thousand and forty four fulfilled the Rheumatology criteria, giving a point prevalence of symptomatic knee OA 19.6%. The prevalence was 21.5% among females and 17.5% among males giving a female bias in the ratio of 1.2:1 (Akinpelu, Alonge, Adekanla and Odole, 2009). Knee OA patients suffer from a combination of joint pain, stiffness, instability, swelling and muscles weakness. This leads to a decrease in quality of life, activities of daily living (ADL) and an increase of medical services consumption in the community. Knee OA is one of the world's common musculoskeletal disorders. Eighty percent of patients with OA of the knee suffer from decrease in mobility while 20% of them suffer an inability to perform everyday activities (Ebnezar, Nagarathna, Bali and Nagendra, 2011). The most common predisposing factors include: age (with the risk increasing as one grow older) and sex (more prevalent in women than men). Other factors include congenital and acquired presence of bone deformities - some people are born with malformed joints or defective cartilage, knee joint injuries - in sports or from an accident, obesity and overweight, jobs which include tasks that place repetitive stress on the knee and other diseases like diabetes, underactive thyroid, gout or Paget's disease of bone. Age is the most common knee OA risk factor. As stated above, it usually appears after the age of 40. But presently, there have been rare cases occurring before this age. When this condition occurs before 45 years, men are more affected than women. After this age, women are more at risk of developing OA than men. Also, women are more predisposed to obesity, one of the most important osteoarthritis risk factors, and therefore to knee OA. Moreover, female hormones may also provoke its occurrence, for example, the release of hormone relaxin during pregnancy usually make all joint more supple and therefore susceptible to micro-injuries, a factor that predisposes the woman to knee OA in future. Akinpelu, Alonge, Adekanla and Odole (2009) reported the prevalence of knee OA in Nigeria across various age groups and gender as; between age 40-49 years, more females than males are affected; age 50-59 years and 60-69 years, more males than females; while in patients aged 70 years and above, more females than males are affected.

2

Pain, reduced knee range of motion and a general reduction in the patients’ functional status, summarizes the effect of this disease. Pain is a subjective phenomenon that varies from one person to the other and with each painful experience, a situation that make its measurement difficult. However, many tools have been developed to try and obtain some objective measurements, an example is the pain rating scale which can be visual or verbal, with its scale relying heavily on individual pain perception. Reduced range of motion is interchangeable with reduced joint flexibility and it implies a reduction in movement range possible about a joint. It is either dynamic (active range of motion) or static (passive range of motion) (Arnheim and Prentice, 1999). Assessment of the static flexibility is widely endorsed as it takes into consideration joint movement as limited by passive constraints such as joint capsule and connective tissue, but it does not asses the muscle/muscle group’s ability to move the whole body segments throughout the whole range of movement (Corti and Rigon, 2003). The cumulative effects of these symptoms usually lead to the general reduction in function. Osteoarthritis generally does not have any cure, and majority of patients with the disease are only managed in primary care. The management aims to reduce pain and disability as well as to improve function and quality of life (Lange, Vanwanselle, Fiatarone and Singh, 2008; Bezalel, Carmeli and Katz-leurer, 2010). The managements is also either pharmacologic (using drugs) or non-pharmacologic. Drug treatments aim at relieving pain predominantly, and this analgesic effect is often limited by side effects. Unsuccessful clinical trials of disease-modifying OA drugs have contributed to increased interest in non-pharmacologic treatments for the condition (Thomas, Muir, Doherty, Jones, O’Reilly and Bassey, 2002). Physical activity and exercise is considered to be one of the most important nonpharmacological treatments for patients with mild to moderate knee osteoarthritis (Altman, et al, 2001.). Positive effects on pain and function as well as cost-effectiveness have been reported with this form of treatment (Roody, Zhang and Doherty, 2005). Until the mid-1970s, most physicians prescribed rest and reduced physical activity for patients with arthritis, but more recent research has demonstrated that a regular programme of cardiovascular exercise and progressive strength training can lead to improvements in joint symptoms, strength and functions in these patients (Roubenoff, 2003; Vincent and Vincent, 2012). Fitness-related problems common to 3

arthritis—such as flexibility loss, muscle atrophy, weakness, osteoporosis, pain, depression and fatigue—are found to respond favourably to a low to moderateintensity, gradually progressing programme (ACSM, 1997), and for people with knee osteoarthritis, in particular, physical activity has been shown to decrease pain, improve self-efficacy and physical function, and delay disability (Macera, Hootman and Sniezek, 2003). For best therapeutic effect, optimal exercises programme for knee OA should aim at reducing pain and increasing the knee range of movement, as well as improving general function. The programme should also focus on improving aerobic capacity, quadriceps muscle strength, or lower limb performance. These exercises of lower limbs are generally classified as open and closed chain kinetic exercises. Open kinetic chain exercises (OKCEs) are carried out with the distal segment of the extremity free to move while the distal segment is relatively fixed during closed kinetic chain exercises (CKCEs) (Adegoke, 2003). These exercises become beneficial in knee OA management when performed in low-intensity isokinetic training, intermediateintensity circuit training and high-intensity strength and interval training (Roubenoff, 2003). Closed kinetic chain exercises are more effective in improving proprioception functional performances in individuals with knee osteoarthritis (Gbiri, Okafor and Alade, 2013). Transcutaneous electrical nerve stimulation (TENS) in the management of osteoarthritis has been shown to be an effective analgesia when compared to pharmacologic treatment (Pietrosimone, Saliba, Hart, Hertel, Kerrigan and Christopher, 2010). As an adjunct to exercise, TENS has been shown to have no additional benefit (Palmer, Domaille, Cramp, Walsh, Pollock, Kirwan and Johnson, 2014). Neuromuscular electrical stimulation (NMES) on the other hand has not been as widely studied in Nigeria and other countries. Electrical stimulators provide direct, alternating, pulsating and/or pulsed waveform forms of energy. These devices are used to exercise muscles, demonstrate a muscular response to nerve stimulation, relieve pain, relieve incontinence, and provide test measurements. Electrical stimulators may have controls for setting the pulse length, pulse repetition frequency, pulse amplitude, and triggering modes. Electrodes for such devices may be in-dwelling, transcutaneous implanted or surface. NMES involves sending of small amount of electrical impulses through the skin to the underlying motor units (nerves and muscles) to produce involuntary muscle contraction. Its goal is to promote re-innervations, to prevent or retard disuse atrophy, 4

to relax muscle spasms, and to promote voluntary control of muscles in patients who have lost muscle function due to surgery, neurological injuries, or disabling condition (Hayes, 2008). In essence, NMES does to the affected limb; the same thing exercise will do voluntarily. A study of the use of home-based NMES for the purpose of improving quadriceps strength in older adults with knee osteoarthritis has produced promising results (Carol, 2006). The gap in the evidence of relative efficacy of NMES in the management of OA and the need to find a substitute or an adjunct to exercise are reasons for the researcher’s desire to study the relative efficacy of NMES, exercise and conventional physiotherapy on patients with this condition in the major hospitals in Abeokuta - the largest city and capital of Ogun state in South-West, Nigeria. Founded in 1825, the city is 77 kilometres by rail and 130 kilometres by water from Lagos, and with a population of 593,140 (in 2006), has two major hospitals - State Hospital and Federal Medical Centre, located on either end of the same road - Olabisi Onabanjo Way. These two hospitals have fully functional Orthopaedic and Physiotherapy departments with the personnel that go with it. Statement of the problem Osteoarthritis is a chronic degenerative joint disease that compromises the quality of life of many people worldwide. The most common type of arthritis occurring in the knee, is OA It is highly prevalent within the general population, and several eminent clinical bodies have produced guidelines for its treatment with emphasis of treatment placed on patient education, pain relief and exercise. Several other studies had been conducted to investigate the benefits of exercises alone, and/ or in combination with other treatment options. Some of these studies reported additional benefit with combination therapy especially at improving the range of motion and reducing pain in the affected knee (Silva, Valim, Pessanha, Oliveira, Myamoto, Jones and Natour, 2008) and some reported no extra benefits (Foster, Thomas, Barlas, Hill, Young, Mason and Hay 2007). The exercise so employed by the reviewed studies were structured in a way that discouraged its use by practitioners, they were cumbersome and not time efficient. Most therapists often had to make use of combination of many treatment modalities, resulting in waste of time and energy. Few of these studies looked into the role of electrical stimulation, a modality whose effects are in resemblance with exercises. Evidence for comparative effect of NMES and exercises on osteoarthritis in literature and studies is insufficient. This study hence aimed to bridge that gap in knowledge and 5

provide kinetic chain exercise programmes that take into consideration, the principles of exercise prescription, and, that can easily be adopted for clinical uses. Objectives of the study The general objective of this study was to compare the effects of neuromuscular stimulation and kinetic chain exercises in the management of knee osteoarthritis. The specific objectives were: i.

To establish the effects of 12 weeks neuromuscular electrical stimulation (NMES) on functional status of patients with knee osteoarthritis.

ii.

To establish the effects of 12 weeks kinetic chain exercise training programme for patients with knee OA on their functional status.

iii.

To justify the effects of 12 weeks NMES and kinetic chain exercises training programme for patients with knee OA on their functional status.

Research questions The research was designed to answer the following questions: 1. What are the pre and post-test pain intensity, range of motion and functional status of patients with knee osteoarthritis across the two experimental and control groups? 2. What are the pre and post-test pain intensity, range of motion and functional status of patients with knee osteoarthritis in relation to: a)

Gender?

b)

Age?

Hypotheses The following hypotheses were tested: 1)

There is no significant main effect of treatment on pain intensity, range of motion and functional status of patients with knee osteoarthritis.

2)

There is no significant main influence of gender on pain intensity, range of motion and functional status of patients with knee osteoarthritis.

3)

There is no significant main influence of age on pain intensity, range of motion and functional status of patients with knee osteoarthritis.

4)

There is no significant interaction effect of treatment and gender on pain intensity, range of motion and functional status of patients with knee osteoarthritis.

5)

There is no significant interaction effect of treatment and age on pain intensity, range of motion and functional status of patients with knee osteoarthritis. 6

6)

There is no significant interaction influence of gender and age on pain intensity, range of motion and functional status of patients with knee osteoarthritis.

7)

There is no significant interaction effect of treatment, gender and age on pain intensity, range of motion and functional status of patients with knee osteoarthritis

Delimitation of the study The study was delimited to the following:

a) Pretest-posttest randomized group research design b) Participants: i.

Patients diagnosed with knee osteoarthritis- unilateral or bilateral.

ii.

Ages- 18 years and above.

c) Government hospitals with established orthopaedic units in Abeokuta, Ogun state, namely- Federal Medical Centre and General Hospital, both in Abeokuta

d) Instruments and Procedure: i.

Electrical stimulator

ii.

12 weeks training programme for patients with knee OA, adapted from exercise for Knee Osteoarthritis and Joint Pain (Andrew, 2011). (Appendix ii a)

iii.

Techniques

of

progressive

resistance

exercise

(DeLorme

&

Watkin,

1948).(Appendix ii b) iv.

Infrared lamp

v.

Goniometer

vi.

Visual analogue scale (VAS) - Edmonton symptom assessment version

vii.

Arthritis Impact Measurement Scale- short Form (AIMS2-SF)

viii.

Metronome

ix.

Stopwatch

x.

Bicycle ergometer

e) Eight research assistants: Four in each of the hospitals f) Others: i.

Three treatment groups: Electrical stimulator and conventional (NMES + Conventional) therapy, Knee OA exercise and conventional (Exercise + Conventional) therapy and conventional therapy groups.

ii.

Descriptive statistics of frequency, percentages, mean and standard deviation.

7

iii.

Inferential statistics of correlated sample t-test and Analysis of Covariance (ANCOVA) with alpha level set at 0.05 Limitation of Study There was subject mortality within the study period, probably because of the fifty two days Nigeria Medical Association’s industrial action that took place during the period. Out of seventy three (73) participants who were originally recruited for the study, only sixty (60) completed their treatments. Also, getting the participants down three times weekly was difficult, but, the number of participants recruited for the study was quite large and each consented participant submitted his/her phone number(s) and that of his/her care giver at the commencement of treatment. Therefore, each of them was contacted a day before the scheduled treatment and the cost of their transportation for the treatment was subsidized to encourage them. To prevent interference with the study, the participants were also encouraged not partake in any other treatment other the ones in the intervention. Significance of the Study Despite the availability of evidence of efficacy of exercises in the management of osteoarthritis, either alone or as an adjunct to other treatment, the available exercise programmes are cumbersome with little attention paid to training procedures. This study has provided additional information on usefulness of exercises in the management of knee OA, together with well-structured 12-week kinetic chain exercise training programme, which the researcher hope will be useful to the managers of this condition. It was also expected that, the 12-week kinetic chain exercise training and techniques of progressive resistance exercise may become the standard exercise programme for knee OA management. There was inadequate information on the usefulness of neuromuscular stimulation in the management of knee osteoarthritis. A clinical evidence of the effectiveness of neuromuscular electrical stimulation in the management of OA of the knee has now been provided and, this could become the required alternative to exercises, most especially in patients with acute onsets in which the smallest of all movement in the affected knee could produce excruciating pain. The researcher also hoped that 12-week NMES may become an adjunct treatment procedure to other methods in improving knee OA patients’ functional status. This 12-week NMES could become the standard neuromuscular stimulation programme, especially in cases where exercise becomes too painful to perform. 8

Finally, because the treatments proposed for this study were structured in a way that basic principles of exercise prescription play major role, the researcher expected that they might help in reducing the treatment and waiting time of patients who are suffering from knee OA if they are adopted for clinical uses. Operational Definition of Terms Closed chain kinetic exercises: Lower limb exercises performed with the distal part of the leg relatively fixed to the floor. Conventional therapy: Thermotherapy with infrared radiation and/or cryotherapy with ice, massage with analgesic ointment, passive mobilization of knee and bicycle ergometry, all embedded within 30-60 minutes time frame per session. Goniometry: Measurement of knee movement passively from knee extension to flexion with a standard goniometer. Kinetic chain exercise: an interval training programme (adapted) which comprises seven types of standard open and closed chain kinetic knee exercises with periods of rest in-between exertions. Knee osteoarthritis: a condition in which the natural cushioning between joints (cartilage) wears away, resulting in pain, swelling, stiffness, reduction in range of movement and, sometimes, the formation of bone spurs. Open chain kinetic exercises: lower limb exercises performed with the distal part of the leg hanging freely from the floor. Pain rating: Subjective measurement of knee pain using a scale called visual analogue scale with the scale readings ranging from 0 (for no pain) to 10 (for the highest pain intensity one has ever been exposed to). Neuromuscular Electrical Stimulation: elicitation of muscular contraction using electric impulse.

9

CHAPTER TWO LITERATURE REVIEW The review of literature for this study was done under the following subheadings: 1.

Conceptual framework for the study

2.

Osteoarthritis: the concept

3.

Osteoarthritis of the knee: 

Overview of knee osteoarthritis



The knee: Anatomy and Biomechanics



Predisposing factors



Epidemiology of knee osteoarthritis



Pathophysiology of knee osteoarthritis



Diagnosis of knee OA



Clinical features of knee osteoarthritis:

i)

Pain

ii)

Flexibility



Management of Knee osteoarthritis:

i)

Pharmacological treatment

ii)

Non- pharmacological treatment:

4.



Neuromuscular electrical stimulation



Exercise

Appraisal of reviewed literature

10

CONCEPTUAL FRAMEWORK FOR THE STUDY

Independent variables

Moderating variables

Dependent variables

Functional status of Knee OA patient

NEUROMUSCULAR ELECTRICAL STIMULATION MALE FEMALE

EXERCISES

Range of Motion

AGE CONVENTIONAL THERAPY

Pain Intensity

CONVENTIONA L THERAY Fig. 2. 1: conceptual framework for the study Source: Self-developed

The conceptual framework on which this study as presented on Fig. 2.1 consists of independent variables, NMES which is going to be generated by electrical stimulators, Exercise - 12 weeks training programme for patients with knee OA and Conventional therapy for knee OA as explained under operational definition of terms. 11

The dependent variables are the effects the three treatments are expected to have on the subjects as measured by AIMS2-SF for functional status, Goniometer for passive range of movement (ROM) and Visual analogue scale (VAS) for pain intensity. The moderator variables include the genders and age of the subject. Osteoarthritis: The Concept Osteoarthritis (OA) is the most common musculoskeletal disorder, characterized by degeneration of articular cartilage, joint space narrowing, pain and disability (O’Reilly and Doherty, 2003). OA of the knee is the most common of all arthritis representing a major contribution to the burden of physical disability, particularly in the elderly (Creamer, Lethbridge-Cejku and Hochberg, 2000). More disability and clinical symptoms result from OA of the knee than from any other joint (Deyle, Allison, Matekel, Ryder, Stang, Gohdes, Hutton, Henderson, and Garber, 2005). The articular cartilage does not contain nerve endings, so it cannot generate pain (Doherty, 2001); hence, the pain of OA arises as an indirect consequence of the damage to the cartilage. In other words, those surrounding tissues that have nociceptors can give rise to pain when distorted by the presence of osteophytes, the loss of normal joint structures and the development of joint instability (Doherty, 2001). 

Definition Osteoarthritis is derived from three Greek words - “Osteo” meaning bones, “arthro” meaning joint and “itis” meaning inflammation. It is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone (Devaraj, 2011). The cartilage normally serves as a pad or a bearing in the joint and when this wears away, the result is a roughed joint surface that causes the pain and stiffness that people associate with osteoarthritis Osteoarthritis of the knee 

Overview of knee Osteoarthritis The chance of developing the disease increases with age. Most people over age

60 have OA to some degree, but its severity varies as even those in their 20s and 30s can have it, and, in people over 50years of age (Oniankitan, Houzou, Koffi-Tessio, Kakpovi, Fianyo, Tagbor and Mijiyawa, 2009). Osteoarthritis of the knee increases in prevalence with age and is also more common in women than in men. The disease can be part of a generalized diathesis, including osteoarthritis of the hand, which may be inherited. The natural history of OA of the knee varies highly, with the disease

12

improving in some patients, remaining stable in others, and gradually worsening in others. It is a leading cause of impaired mobility in the elderly with many persons with knee pain having limitations in function, which prevent them from engaging in their usual activities (Felson, 2006). Although there is no cure for OA, there are many treatment options available to manage the patient’s pain and make them to keep active. These treatments are broadly classified into pharmacologic, which involve drug ingestion, and non-pharmacologic, which has exercises as an important example. 

The knee: Anatomy and Biomechanics The knee is one of the largest and most complex joints in the body. It joins the

thigh with the lower leg, consisting of two articulations: one, between the femur and tibia, and the other one, between the femur and patella. The joint is synovial, comprising a convex femoral end superiorly and a concave tibial end inferiorly. The smaller bone that runs alongside the tibia (fibula) and the kneecap (patella) are the other bones that make the knee joint. It is the largest joint in the human body and is very complicated. The knee is a pivotal hinge joint, which permits flexion and extension as well as a slight medial and lateral rotation. Tendons connect the knee bones to the leg muscles that move the knee joint. Ligaments join the knee bones and provide stability to the knee (Grays, 1918): -

The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).

-

The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur).

-

The medial and lateral collateral ligaments prevent the femur from sliding side to side. Two C-shaped pieces of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia. Numerous bursae, or fluid-filled sacs, help the knee move smoothly. The whole joint is enclosed in fibrous sac - the capsule, which is filled with fluid-synovial fluid, required for the joint lubrication (Pietrosimone, et al, 2010). It plays an essential role in movement related to carrying the body weight in horizontal (running and walking) and vertical (jumps) directions. Anterior to the knee joint is the knee cap, a sesamoid bone called patella. At birth, a baby will not have a conventional knee cap, but a growth formed of cartilage. By the time the child is 3-5 years of age, ossification will have replaced the cartilage with bone. Because it is the largest sesamoid bone in the human body, the ossification process significantly takes longer (Ogden, 2009). 13

Movement of the knee joint can be classified as having six degrees of freedom - three translations: anterior/posterior, medial/lateral, and inferior/superior and three rotations:

flexion/extension,

internal/external,

and

abduction/adduction.

The

movements of the knee joint are determined by the shape of the articulating surfaces of the tibia and femur and the orientation of the four major ligaments of the knee joint: the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments as a four-bar linkage system (Palmer, 2009).

Fig 2.2: The ligaments of the knee (arrow shows direction of “screw home mechanism”)

Plate 2.1: Saggital MRI scan showing the anterior (small arrow) and posterior cruciate ligaments (large arrow) ACL and PC Knee flexion/extension involves a combination of rolling and sliding called “femoral roll back” which is an ingenious way of allowing increased ranges of flexion 14

(Fig 2.3). Because of asymmetry between the lateral and medial femoral condyles, the lateral condyle rolls a greater distance than the medial condyle within 20 degrees of knee flexion. This causes a coupled external rotation of the tibia which has been described as the “screw-home mechanism” of the knee which locks the knee into extension (Fig 2.2). The anterior cruciate ligament drives this “screw home mechanism” and absence of this control is the basis of the pivot shift test of an ACL deficient knee.

Fig 2.3: The Movements of the knee The primary function of the medial collateral ligament is to restrain valgus movement of the knee joint with its secondary function being control of external rotation. The lateral collateral ligament restrains against varus movement as well as resisting internal rotation. The primary function of the anterior cruciate ligament (ACL) on the other hand is to resist anterior displacement of the tibia on the femur when the knee is flexed and control the screw home mechanism of the tibia in terminal extension of the knee. A secondary function of the ACL is to resist varus or valgus rotation of the tibia, especially in the absence of the collateral ligaments. The ACL also resists internal rotation of the tibia. The main function of the posterior cruciate ligament (PCL) is to allow femoral rollback in flexion and resist posterior translation of the tibia relative to the femur. The

menisci

are

intra-articular

crescentic

structures

made

of

elastofibrocartilage. They are important for reducing contact stresses on the articular cartilage, shock absorption, circulation of synovial fluid and joint stability. The medial 15

meniscus is tethered to the deep part of the medial collateral ligament and so it is more prone to injury than the lateral meniscus which is more mobile. The lateral meniscus is smaller than the medial and is sometimes discoid in shape.

Plate 2.2: A normal medial meniscus seen at arthroscopy.

Plate 2.3: A normal smaller lateral meniscus The movement of the patellofemoral joint can be characterized as gliding and sliding. During flexion of the knee the patella moves distally on the femur. This movement is governed by its attachments to the quadriceps tendon, ligamentum patellae and the anterior aspects of the femoral condyles. The muscles and ligaments of the patellofemoral joint are responsible for producing extension of the knee. The patella acts as a pulley in transmitting the force developed by the quadriceps muscles to the femur and the patellar ligament. It also increases the mechanical advantage of the quadriceps muscle relative to the instant centre of rotation of the knee.

16

Plate 2.4: The patellofemoral joint as seen on a Sagittal MRI scan (arrows mark the patella and patella tendon)

The mechanical axis of the lower limb is an imaginary line through which the weight of the body passes. It runs from the centre of the hip to the centre of the ankle through the middle of the knee. This is altered in the presence of deformity and must be reconstituted at surgery (see Plate 2.5). This allows normalization of gait and protects the prosthesis from eccentric loading and early failure.

Plate 2.5: A long leg view demonstrating abnormal mechanical axes with the line of body weight passing through the medial side of the knee.

17

Osteoarthritis of the knee is the most common type of arthritis. In this disease, the cartilage in the knee gradually wears away. The disease was significantly commoner among Nigerians than Caucasians below the age of 50 years (Ebong, 1985). Knee osteoarthritis is caused by cartilage breakdown in the knee joint. 

Predisposing factors Several factors have been implicated in the pathogenesis of OA (Rubinow, 1998).

This risk factor can be classified as either primary or secondary. The primary risk factors are: age, gender, obesity, genetics, bone density, hormonal status and ethnicity while the secondary factors are: trauma, occupation, nutritional factors, exercise and sports, knee alignment and smoking (Doherty, 2001). However, in some cases, one group of risk factors may become dominant over the others, thus supporting the theory that OA is a disease spectrum with no case attributable to a single risk factor (Hochberg, Letherbridge-Cejku, Plato, Wigley and Tobin, 1991). Most currently recognized risk factors for prevalent knee OA (obesity, knee injury, and physical activity) influence incidence more than radiographic progression. Evidence of age-related changes in the function of chondrocytes suggests that age-related changes in articular cartilage could contribute to the development and progression of OA (Bulkwalter and Mankm, 1998). Age This is the most common osteoarthritis risk factor. As stated above, osteoarthritis usually appears after the age of 40. However, there have been cases when it occurred before 40 years, but these cases are rare. Also, while there are proofs that adults of any age can develop this joint disease, the prevalence of symptomatic knee OA increases rapidly starting from age 45 and continue to increase thereafter. The prevalence increases with age, the knee joint experience an increasing wear and tear, cartilage thins and becomes less flexible, making it more prone to degeneration, and for this reason the condition is also called degenerative joint disease. In a study conducted by Losina et al (2013), the diagnosis of symptomatic knee OA was concluded to occur early in life with estimated highest incidence occurring among people aged 55-64 years in the US, suggesting that prevention should be offered early in the course of life. Gender There is some evidence that women have higher rates of incident knee OA than men as they age. In cases when osteoarthritis occurs before 45 years, men are more affected than women. After this age, women are more predisposed to osteoarthritis than 18

men. Also, women are more predisposed to obesity, one of the most important osteoarthritis risk factors, and therefore to osteoarthritis. Data from the Framingham Knee Osteoarthritis Study, a population-based study of osteoarthritis, reported a higher incidence of osteoarthritis of the knee in women than in men. Similarly, women were estimated to have a lifetime increased risk of symptomatic knee osteoarthritis (Guccione et al, 1994). The reasons for this difference are not completely clear, but an increase in osteoarthritis observed in women at the time of menopause has led to the hypothesis that hormonal issues may play a role in the development of osteoarthritis. However, results from both observational studies and larger randomized trials on the association of oestrogen and osteoarthritis have been mixed. In the Women’s Health Initiative, a randomized double-blind, placebo-controlled trial of oestrogen replacement (Cirillo, Wallace, Wu and Yood 2006), oestrogen supplementation was found to be associated with a slightly significant decreased rate of either hip or knee arthroplasty, but the hazard ratios were insignificant in individual analysis of hip and knee arthroplasty. While these results are of interest, the association of oestrogen and incident knee and hip osteoarthritis is still not clearly defined. In a study of relationship between biochemical markers of arthritis and the radiographic grading of knee OA, female gender was a strong risk factor even in the subgroup without radiographic knee OA. For instance, the greater total body fat of the average adult female may partially account for the gender disparity toward OA. Given that females theoretically demonstrate higher levels of adipose-derived systemic leptin concentrations than their male counterparts, female gender increases the risk of knee OA (Heidari, 2011). Obesity Overweight and obesity are the most common osteoarthritis risk factors found particularly in women. Obesity is a chronic condition that develops as a result of an interaction between a person's genetic makeup and their environment. How and why obesity occurs is not well understood, however, social, behavioural, cultural, psychological, metabolic, and genetic factors are involved (Wolf and Tanner, 2002). This risk factor is mostly a cause for knee osteoarthritis. The surplus of weight stresses the joint more and thus increases the chance of developing osteoarthritis. Also, having excessive fatty tissue may result in an early development of osteoarthritis or a more rapid progression of an existing one. Moreover, obesity may also cause more severe pain in case of hip and knee osteoarthritis. Obesity has been shown to be 19

associated with an increased risk of incident knee osteoarthritis in several studies. A study from Finland reported on 823 subjects without baseline knee osteoarthritis, and a strong association with incident knee osteoarthritis and BMI was found, adjusting for age and gender, and a higher odds ratio for subjects in the highest categories of BMI (BMI = 25–29.9 or >30.0) compared to subjects with BMI