The role of the deep medial collateral ligament in ...

Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3095-1

KNEE

The role of the deep medial collateral ligament in controlling rotational stability of the knee Etienne Cavaignac • Karel Carpentier • Regis Pailhe´ • Thomas Luyckx • Johan Bellemans

Received: 30 October 2013 / Accepted: 22 May 2014 Ó Springer-Verlag Berlin Heidelberg 2014

Abstract Purpose The tibial insertion of the deep medial collateral ligament (dMCL) is frequently sacrificed when the proximal tibial cut is performed during total knee arthroplasty. The role of the dMCL in controlling the knee’s rotational stability is still controversial. The aim of this study was to quantify the rotational laxity induced by an isolated lesion of the dMCL as it occurs during tibial preparation for knee arthroplasty. Methods An isolated resection of the deep MCL was performed in 10 fresh-frozen cadaver knees. Rotational laxity was measured during application of a standard 5.0 N.m rotational torque. Maximal tibial rotation was measured at different knee flexion angles using an imageguided navigation system (Medivision Surgetics system, Praxim, Grenoble, France) before and after dMCL resection. Results In all cases, internal and external tibial rotation increased after dMCL resection. Total rotational laxity increased significantly for all knee flexion angles, with an average difference of ?7.8° (SD 5.7) with the knee in extension, ?8.9° (SD 1.9) in 30° flexion, ?7° (SD 2.9) in 60° flexion and ?5.3° (SD 2.8) in 90° flexion. Conclusions Sacrificing the tibial insertion of the deep MCL increases rotational laxity of the knee by 5°–9°, depending on the knee flexion angle. Based on our findings, new surgical techniques and implants that preserve E. Cavaignac (&) R. Pailhe´ Institut de l’appareil locomoteur, CHU Rangueil, 1, Avenue Jean Poulhe`s TSA 50032, 31059 Toulouse Cedex 9, France e-mail: [email protected] K. Carpentier T. Luyckx J. Bellemans Department of Orthopedic Surgery and Traumatology, University Hospitals Leuven, Louvain, Belgium

the dMCL insertion such as tibial inlay components should be developed. Further clinical evaluations are necessary. Keywords Deep MCL Rotational stability Knee prosthesis Inlay technique

Introduction The deep medial collateral ligament (dMCL) of the knee is located in the third layer of the medial compartment and is divided into meniscofemoral and meniscotibial portions [17, 20, 35, 37]. It is in close contact with the femoral and tibial articular surfaces [32]. As a static secondary stabilizer, the dMCL counteracts rotational forces [12, 31]. Previous studies have attempted to assess the impact of the dMCL on knee stability, but the results are contradictory [11, 31, 36]. Warren et al. [36] found no differences in tibial rotation during torsional movements with or without an intact dMCL. Others authors have shown that the dMCL limits external [11, 13, 31] and internal rotation of the tibia [11]. However, these previous studies on the dMCL were performed without intact tendon and ligament structures around the knee joint [11, 31]. As a consequence, we still do not know how the dMCL contributes to the knee’s rotational stability when the peri-articular soft tissues are intact. Since the tibial insertion of the dMCL is regularly resected when the tibial cut is carried out during total knee arthroplasty (TKA) [25], we wanted to know whether disrupting this ligament affects rotational stability in the knee. Some studies have suggested that rotational instability results in increased wear of TKA polyethylene inserts [3, 5]. Our hypothesis was that dMCL injury leads to rotational instability. This study sought to measure the

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Knee Surg Sports Traumatol Arthrosc

rotational laxity induced by an isolated dMCL lesion at various amount of knee flexion.

Materials and methods Specimen preparation Ten fresh-frozen cadaver knees were obtained from the pathology department of the Catholic University of Leuven: 7 males/3 females; 6 right/4 left; mean age of 81.2 years (72–90). The cadavers were stored at -20 °C and thawed overnight at 2 °C before dissection and subsequent biomechanical analysis. None of the knees showed macroscopic evidence of previous injury, surgery or significant arthritis. All the soft tissues (ACL, PCL, MCL, LCL, meniscus, extensor mechanism, tendons) appeared macroscopically normal and the joint range of motion was normal. A midline skin incision was performed and a medial parapatellar arthrotomy from the superior-medial side of the patella to the tibial plateau, always staying medial of the patellar tendon. The quadriceps tendon was not cut during this approach. The dMCL was first exposed without opening the joint. The dMCL is divided into meniscofemoral and meniscotibial portions [18, 21, 32, 35, 37]. The ligament was exposed by developing the plane between the superficial and deep MCL (Fig. 1) [32]. Great

care was taken not to cut the superficial MCL, which is separated from the deep MCL by a bursa [19, 32]. The landmarks required for the navigation system were located. At the end of the experimental procedures, the superficial MCL was resected to verify whether the dMCL had been completely resected. If it had not, the cadaver specimen was excluded from the results. Testing system An image-guided surgical navigation system (Medivision Surgetics System, Praxim, Grenoble, France) was used to measure femoral and tibial displacements (Fig. 2). This system measures knee flexion and internal–external rotation. The reproducibility of this system has previously been demonstrated; its accuracy is 0.1 mm for linear measurement and 0.1° for angular measurements [28]. The cadaver was placed in a supine position. The ankle was disarticulated, the malleoli (navigation landmarks) were left intact and the inferior part of the articular surface of the tibia was exposed. A 12-mm-diameter rod was pressfit into the distal tibia shaft [15]. A 25 N.m torque wrench (BGS technic KGÒ, Wermelskirchen, Germany) was used to apply a 5 N.m rotational torque to the tibia [10, 11, 15, 24, 31] (Fig. 3). The knee was fixed either in full extension or 30°, 60° and 90° of flexion with a knee support. Outcomes measures Each knee was tested separately. Before each test, the knee was placed in neutral position as determined by the navigation system. Displacements were recorded during two experimental conditions: with the dMCL intact and then after dMCL resection. External and internal rotation was evaluated in each knee flexion condition after the torque was applied. The rotation was measured by the surgical navigation system during each displacement test. Movements were repeated three consecutive times. The recorded value was the average of these three measurements. Total rotation was defined as the sum of internal and external rotations in knee flexion condition. The research ethics committee at the UZ Leuven (Universitaire ziekenhuizen Leuven) approved this study. Statistical analysis

Fig. 1 Dissection photograph showing the deep MCL (full arrow) located under the superficial MCL (empty arrow). The deep MCL was exposed by developing the plane between the two ligaments with dissecting scissors

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Based on the Griffith et al. study [11], the difference in external rotation at 30° flexion was estimated to be 5° and the standard deviation 2.75°. With a power of 80 % and an alpha of 0.05, a minimum sample size of ten knees was required to detect this difference. To validate the experimental design, measurements were repeated on 10 specimens for a complete intact testing sequence at

Knee Surg Sports Traumatol Arthrosc Fig. 2 Testing system. A standard navigation protocol was carried out. Femoral and tibial reference arrays containing three infrared reflective spheres were attached to the femur and tibia, with two 3-mm-diameter threaded pins used for each array. A pointer with three infrared reflective spheres was used to mark the middle of the intercondylar notch, intercondylar eminence, centre of both tibial plateaus, middle of the anterior intermeniscal ligament and two malleoli. The camera arm was placed about 1.5 m lateral to the tibial and femoral arrays

?1) between two metric measurements was calculated along with their level of significance. Normal distribution of continuous variables was verified using the Shapiro– Wilk test and equality of variances was evaluated using Fisher’s F test and Levene’s test to determine whether the assumptions had been met for use of parametric tests. Descriptive data analysis was performed using Student’s t test. The differences between intact and resected dMCL data for each flexion angle were analysed with the paired Student’s t test. Total rotation was calculated. The difference in rotation after sectioning the dMCL was expressed as a percentage of intact MCL rotation values. A significant difference was defined as P \ 0.05. All statistical analyses were carried out by an independent statistician using EXCELÒ (Microsoft Inc., Redmond, WA, USA), SPSSÒ (SPSS Inc., Chicago, IL, USA) and STATA SE v11.0 (StataCorp LP, College Station, TX, USA) software.

Results Fig. 3 Reproducible 5 N.m rotational force achieved with a torque wrench

all knee flexion angles. We carried out correlation matrices with Pearson’s correlation tests to determine the validity of intraspecimen measurements. These tests were interpreted according to Landis and Koch’s recommendations. The strength of the correlation (between -1 and

Validation The average Pearson’s coefficient was 0.95 (SD = 0.025). The reproducibility of the biomechanical testing apparatus, navigation system measurements, ligament properties and external load application was high. Table 1 shows the values for the different test conditions. The average angular difference between the two trials was 0.9° ± 1.2° when

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Knee Surg Sports Traumatol Arthrosc Table 1 Validation of the experimental design External rotation

Internal rotation

Value

CI

Value

CI

Extension

0.97

0.73–0.99

0.92

0.69–0.98

Flexion 30°

0.92

0.7–0.97

0.97

0.74–0.99

Flexion 60°

0.98

0.8–1

0.93

0.82–0.97

Flexion 90°

0.97

0.87–1

0.91

0.74–0.95

Mean

0.95

SD

0.025

Reproducibility of the testing system measurements based on Pearson’s coefficient CI 95 % confidence interval

external rotation torque was applied and 0.8° ± 1° with internal rotation torque. Internal and external rotation The internal and external rotation values before and after the dMCL resection are shown in Fig. 4. All of the values were significantly different after the resection, except for internal rotation at 60° flexion. Comparative analysis showed that all rotational values increased after dMCL resection. The external rotation at 30° flexion increased by 5.6° (SD 2) (P \ 0.05). The mean total rotational laxity increased significantly for all knee flexion angles: ?7.8° (SD 5.7) with the knee in extension, ?8.9° (SD 1.9) in 30° flexion, ?7° (SD 2.9) in 60° flexion and ?5.3° (SD 2.8) in 90° flexion. Table 2 shows the rotation values for the various knee flexion conditions. Figure 5 presents the relative increase in rotation as percentage of initial rotation. The relative increase was less as the flexion angle increased. In full extension, rotation increased 43 % (SD 31) after the dMCL was resected; at 90° flexion, the rotation increased by only 16 % (SD 8) (P \ 0.05). Fig. 4 Mean rotation measurements (°) obtained with the standardised load at various flexion angles. Grey Intact dMCL, Black resected dMCL. SD Standard deviation, Ext Rot external rotation, Int Rot internal rotation, Tot Rot total rotation. The only nonsignificant difference is noted with a star (*)

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Table 2 Change in rotation (degrees) between the dMCL intact and dMCL resected conditions at each knee flexion position

Ext Rot Int Rot Tot Rot

Extension

Flexion 30°

Flexion 60°

Flexion 90°

D

D

D

P value

D

\0.05

3.2 \0.05

0.06

2.1 \0.05

\0.05

5.3 \0.05

P value

P value

3.0 \0.05

5.6 \0.05

4.0

4.8 \0.05

4.3 \0.05

3.4*

7.8 \0.05

8.9 \0.05

7.0

P value

P values correspond to Student’s t test. The only non-significant difference is noted with a star (*) Ext Rot External rotation, Int Rot internal rotation, Tot Rot total rotation, D difference

Discussion The most important finding of the current study was the increased amounts of internal and external rotation throughout the knee flexion range after isolated dMCL resection. There was a difference of more than 5° external rotation at 30° flexion between conditions where the deep MCL was intact or resected (P \ 0.05). The maximum difference in external rotation was obtained at 30° flexion while the maximum difference in internal rotation was found in extension. The relative increase in rotation values obtained after dMCL resection was less with flexion (Fig. 4). Therefore, the dMCL has a key role in rotational stability in extension and early flexion. It has a relatively less important role in deeper flexion. To our knowledge, the current study is the only one to evaluate the effect of an isolated lesion of the deep MCL. Complete cadavers were used and all soft tissue remained intact, so as to reproduce an isolated deep MCL injury. Few studies have evaluated the deep MCL’s contribution to knee stability, especially during rotational movements.

Knee Surg Sports Traumatol Arthrosc Fig. 5 Percentage increase in rotation for the different knee positions. All values were statistically significant except internal rotation at 60° of knee flexion*. Ext Rot External rotation, Int Rot internal rotation, Tot Rot total rotation

Griffith et al. [11] and Robinson et al. [31] found that the deep MCL is a constraint for external rotation. Griffith et al. also found an increase in internal rotation after resecting the two bundles of the deep MCL [11]. Haimes et al. [13] stated that the deep MCL has no role in the rotational stability of the knee, but did not directly evaluate this possibility. In a cadaver study with 18 knees, sequential dissection found no measurable increase in internal rotation after the deep MCL was cut [31]. However, the rotation was not measured with a navigation system. The difference in rotation (with and without deep MCL) was less in the current study than in the Griffith et al. study [11]. This can probably be explained by the fact that all the muscles around the knee were detached and the condition of the medial meniscus was not described (resected or not). Levy et al. [23] have shown that the meniscus and patella are involved in knee stability. Since fresh-frozen cadavers were used in the current study, the preparation technique does not alter ligament and muscle tissues [38]. We believe that the current study design more realistically stimulates the expected in vivo effect of an isolated dMCL injury. Despite the care taken to avoid detaching the meniscus, resection of the dMCL may have compromised the meniscus. Nonetheless, this would not explain the increased internal rotation observed in the study. Like Ho et al. [15], the rotational force was directly applied to the tibia by inserting an intramedullary rod after ankle disarticulation; this prevents force dissipation due to ankle rotation [1, 2]. Measurements were performed after a full dissection in both conditions; thus, the only difference between the two conditions was the status of the dMCL. Since the aim of the current study was to evaluate the role of the dMCL in controlling rotational stability, we did not evaluate other parameters such as frontal plane stability

as this is a non-controversial topic. All studies evaluating the role of the dMCL in frontal plane stability have shown that the dMCL acts as a secondary stabilizer during valgus loading [11, 31]. Stability in the frontal plane induced by correct ligament balancing is a key element of a successful knee arthroplasty [8, 30, 34, 39]. The main limitation of the current study was that experimental studies evaluate only passive stabilizers, not active ones, which limit the conclusions that can be drawn about the potential consequences of an in vivo lesion [31]. Moreover, some component of the rotational instability observed after dMCL lesion may be related to the medial meniscus being partially released. These two structures are very closely related to each other [20, 32]. The medial meniscus plays a role in the rotational stability of the knee [16, 17, 29]; when it is injured, external rotation increases [14]. Furthermore, the arthrotomy was not reclosed between the two test conditions because it was not possible to ascertain whether the suturing tension was equal, which could have been a confounding factor when interpreting the results. Rotational instability increases polyethylene wear [3, 5]. However, the clinical consequences of dMCL resection on knee arthroplasty still need to be determined because the correlation between instrument-based and manual clinical evaluations is not proven [4]. Maes et al. showed that the dMCL insertion is resected when a standard 9-mm bone cut is made to implant the tibial component of a TKA. On average, only 54 % of the tibial insertion is preserved; it is completely resected in 29 % of cases [25]. The dMCL lies in very close proximity to the joint area of both the femur and tibia [18, 22, 37]. The MCL’s femoral insertion is located on an average of 15 mm from the femoral articular surface and 2–3 mm from the tibial articular [32]. It seems difficult to preserve the tibial and meniscal components of the dMCL when standard surgical techniques are used.

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Tibial preparation for an inlay-type UKA or TKA could preserve the medial cortex of the tibia and thereby the deep MCL insertion site [6, 7, 27, 33]. Similarly, an implant design that requires less bone resection could protect the MCL’s tibial insertion site. Theoretically, an all-polyethylene tibial component could achieve this goal. It has been shown that the survival of all-polyethylene tibial components is comparable to metal-backed components [9, 26].

Conclusion In this study, greater external rotation was found at 30° and 90° of knee flexion after the deep MCL is injured. Although the dMCL is only a secondary knee stabilizer, it has a significant role in the knee’s rotational stability. By injuring this ligament, instability is induced in internal and external rotation in a cadaver model. Further studies need to be conducted to determine whether this holds true in a clinical setting. Conflict of interest No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

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