effectively seal the femoral canal and reduce the rate of radiolucent lines and endosteal osteolysis (6, 7). The Sum- mit stem also has different offset options.
Hip Int 2010 ; 20 ( Suppl 7 ): S63-S69
primary THA
Multicentric and prospective study of the Summit cementless stem Eduardo García-Cimbrelo 1, Antonio Bru-Pomer 2, Boris García-Benítez 3, Moisés Hernández-Blanco 4, Javier Vaquero 5 Orthopaedic Department, Hospital La Paz, Madrid - Spain Orthopaedic Department, Hospital General, Valencia - Spain 3 Orthopaedic Department, Hospital San Juan Dios, Sevilla - Spain 4 Orthopaedic Department, Hospital Meixoeiro, CHUVI, Vigo - Spain 5 Orthopaedic Department, Hospital Gregorio Marañón, Madrid - Spain 1 2
Abstract. We assess early clinical and radiographic results of a multicentric and prospective study of 485 Summit porous-coated stems implanted in 5 hospitals. Of the patients, 171 had a hydroxyapatite (HA) coating and 314 had non-HA porous-coated stems. The mean follow-up was 4.2 years (range 2.5-6 years). The median size of the stem was 5. A standard femoral offset stem was used in 366 hips (75.5%) and a high femoral offset in 119 hips (24.5%). Dislocation was the most frequent postoperative complication (16 hips). Clinical results according to the Harris scale were 30.17 points (range 10-52) before surgery and 95 points (range 90-100) at the last follow-up evaluation. All stems were radiographically osseointegrated. Femoral stem position was neutral in 395 hips (81.4%), and femoral canal filling was related with implant position. No stem subsidence greater than 5 mm has been found in any hip. No osteolysis was found around the femoral stem. No differences have been found between HA coating and non-HA porous-coated stems. Although the present follow-up in this series is too short to allow definite conclusions, the Summit stem with and without HA coating has provided excellent short-term results. Key Words. Cementless tapered stem, Hip prosthesis, Summit
INTRODUCTION Although the clinical results at 10 years with a tapered stem are generally excellent, bone remodelling changes and proximal radiolucent lines and osteolysis are not uncommon (1-5). The Summit tapered titanium stem is made with a porous coating to favour bone ingrowth that will effectively seal the femoral canal and reduce the rate of radiolucent lines and endosteal osteolysis (6, 7). The Summit stem also has different offset options. Increasing the
femoral offset lengthens the leverage for the abductor muscles, resulting in lower joint reaction forces (8), producing greater hip abduction motion and abductor muscle strength (9), and also a reduction in polyethylene wear (10). The benefits of adding a hydroxyapatite (HA) coating to a cementless stem are well known (11-16). In this study we hypothesised that the Summit porouscoated tapered stem (DePuy, Johnson & Johnson, Warsaw, IN, USA) would allow us to obtain excellent clinical results and radiographic ingrowth with a better seal of the
© 2010 Wichtig Editore - ISSN 1120-7000
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The Summit cementless stem
femoral canal and thus reduce the incidence of radiolucent lines, subsidence, and endosteal osteolysis. We assess early clinical and radiographic results of the Summit tapered stem from a multicentric and prospective study. We also compare the same porous-coated stem with and without HA coating.
MATERIAL AND METHODS We prospectively followed 485 hips (in 468 patients) with a primary Summit cementless stem implanted between October 2003 and July 2007 at 5 institutions. Of the patients, 171 had HA coating and 314 had non-HA porous-coated stems (PC). Patients’ sex, age, side, femoral bone quality, activity, and diagnoses are detailed in Table I. The activity level was classified on the Devane et al (17) scale, and femoral canal shape was classified according to Dorr et al (18) as type A (funnel-shaped), type B (intermediate), or type C (cylindrical). Of the 485 hips, 21 hips were lost to follow-up evaluation because the patients had either died (4 patients TABLE I - PATIENT DETAILS (n=485) Side, right/left Sex, male/female Mean age in years (range)
257/228 235/250 65.1 (18-84)
Activity level, Devane et al (17) Level 1
58
Level 2
112
Level 3
144
Level 4
146
Level 5
25
Bone type (18) Type A
153
Type B
272
Type C
60
Diagnosis Osteoarthrosis
357
Avascular Necrosis
40
Dysplasia arthritis
17
Posttraumatic arthritis
35
Developmental arthritis
13
Inflammatory arthritis
17
Other
6
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Fig. 1 - Photograph showing a view of a Summit femoral stem. It is made of a titanium alloy without the hydroxyapatite metaphyseal coating. The tapered stem and proximally located ZTT steps improve load transfer to the bone, reduce hoop stress on the femur, and resist subsidence.
despite a good clinical result) or been lost to follow-up (17 hips). The remaining 464 hips (94 patients) formed the basis of the follow-up study. For these 464 hips, the minimum clinical and radiographic follow-up at the last evaluation was 2.5 years (mean 4.2 years; range 2.5-6 years). Oral and written informed consent was obtained from all patients, and they were also informed preoperatively that they might receive a new stem design without well-known results. The Summit stem is made of titanium and has a taperedstem design with a Porocoat Porous Coating (DePuy, Johnson & Johnson, Warsaw, IN, USA) in the proximal part. The stem length provides 3 point fixations while the conical contact created by the 3-degree proximal to distal taper results in proximal stress transfer (19-21). The tapered stem and the located proximally ZTT steps (DePuy, Johnson & Johnson, Warsaw, IN, USA) located proximally improve load transfer to the bone, reduce hoop stress on the femur, and resist subsidence (22) (Fig. 1). The Summit stem can also have an additional HA coating (Duofix; DePuy, Johnson & Johnson, Warsaw, IN, USA). The neck has offset adjustments that can provide high and low offset stem options and at least 5 modular femoral head lengths without affecting leg length. All Summit femoral components have a 130-degree neck-stem angle. A Duraloc
García-Cimbrelo et al
(with an Enduron polyethylene) or a Pinnacle (with a Marathon cross-linked polyethylene) modular cementless cup (DePuy, Johnson & Johnson, Warsaw, IN, USA) were used in most hips. A ceramic-on-ceramic friction pair bearing surface (Ceramax; DePuy, Johnson & Johnson, Warsaw, IN, USA) was used in 93 hips. We performed all operations with the same technique using a posterior approach. The median diameter of the cups was 52 mm and the median size of the stem 5. A standard femoral offset stem was used in 366 hips (75.5%) and a high femoral offset in 119 hips (24.5%). Two screws for cup fixation were used in 142 hips (29.2%). The surgeons decided on the use of screws depending on the stability of the cup fixation. Stem data are listed in Table II. Postoperatively, all patients received an antibiotic and low-molecular-weight heparin subcutaneously to prevent thromboembolic incidents. Patients walked with toe-touch and partial weight-bearing with crutches for 3 weeks postoperatively, after which they were allowed to walk using 2 crutches for the next 6 weeks. Patients were clinically evaluated for pain, function, and range of motion using the 6-level scale described by Harris (23). Patients were also asked about the location of pain. Standard anteroposterior radiographs of the pelvis and lateral radiographs of the hip were made immediately after the operation, at 6 weeks, at 3, 6, and 12 months, and then annually thereafter following the same protocol. The patient was positioned supine with his or her feet together. The X-ray tube was positioned over the symphysis pubis 1 m from and perpendicular to the table.
TABLE II - STEM CHARACTERISTICS Diameter size
Porocoat stem (n=314)
Duofix stem (HA coating) (n=171)
Total
1 2 3 4 5 6 7 8 9
8 17 42 62 87 64 28 6 -
-5 12 23 45 32 43 9 2
8 22 54 85 132 96 71 15 2
Total
314
171
485
Mean stem size: 4.98 ± 1.26 (range 1-9), median: 5. Mean cervical neck: 7.6 ± 3.68 (range 1.5-15), median: 8.5.
The position of the stem was defined as neutral, valgus (0.3 degree of lateral deviation), or varus (0.3 degree of medial deviation). Femoral canal filling, measured as the ratio of the width of the stem to the width of the medullary canal, was determined at 3 levels: level A (at the metaphyseal part of the stem), level B (at the middle of the stem), and level C (1 cm proximal to the tip). The distribution of any radiolucent lines or osteolysis as seen on the anteroposterior radiographs was recorded in the zones described by Gruen et al (24). Femoral osteolysis was classified according to the criteria described by Goetz et al (25). Femoral osteopaenia resulting from stress shielding was graded according to the system described by Engh et al (26). Femoral component fixation was graded according to the criteria for porous prostheses described by Engh et al (27). Heterotopic ossification was classified according to Brooker et al (28).
RESULTS Intraoperative complications were 7 greater trochanter avulsions and 3 lesser trochanter cracks that were treated using a wire cerclage. There were also 2 lesions of the CPE that partially recovered. Postoperatively, there was 1 infection, which was healed with an early debridement and polyethylene liner change. The most frequent postoperative complication was dislocations (16 hips [3.3%]) that were managed conservatively, and required cup revision in 3 hips. All of these hips later became osseointegrated with good clinical results and were included in the follow-up study. There were 2 cup loosenings requiring cup revision. There were 12 limb discrepancies greater than 1 cm. Clinical results according to the Harris scale were 30.17 points (range 10-52) before surgery, 72.9 points (range 68-90) at 3 months, 83.1 points (range 80-100) at 6 months, and 95 points (range 90-100) at the last follow-up evaluation (Fig. 2). Two patients complained about thigh pain but did not require stem revision. There have been no stem revisions in the follow-up study in this series. All stems were radiographically osseointegrated (Fig. 3). Femoral stem position was neutral in 395 hips (81.4%), varus in 61 (12.6%), and valgus in 29 (6.0%). Femoral canal filling at the immediate postoperative and last evaluation are detailed in Table III. With the number of available hips, femoral canal filling was related with implant position, but not with femur type (Tab. IV). To date, no S65
The Summit cementless stem
TABLE III - FEMORAL CANAL FILLING AT DIFFERENT LEVELS AT IMMEDIATE POSTOPERATIVE AND LAST EVALUATION Post-op
Last evaluation
Level A
84.7 ± 6.8
85.8 ± 6.7
Level B
90.4 ± 7.5
91.1 ± 7.5
Level C
89.7 ± 7.3
90.6 ± 7.3
TABLE IV - F EMORAL CANAL FILLING AT DIFFERENT LEVELS VERSUS FEMORAL TYPE (18) AND VERSUS STEM POSITION (NEUTRAL VERSUS VARUS AND VALGUS POSITION)
Fig. 2 - Boxplot showing preoperative and postoperative clinical results according to the Harris scale at different periods of the follow-up.
stem subsidence greater than 5 mm has been found in any hip. Radiolucent lines have been observed in 18 hips, but these lines were limited to the corner of the upper part of the stem. In every instance, the radiolucencies were 1 mm. Radiodense lines indicating condensed bone were found in 24 hips, around the smooth part of the stem. No
A
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B
Type A
Type B
Type C
p Value
Level A
76.5 ± 11.2
76.2 ± 10.8
76.8 ± 11.5
0.945
Level B
85.3 ± 9.7
81.6 ± 10.4
82.4 ± 11.9
0.055
Level C
81.4 ± 12.1
79.5 ± 14.2
82.4 ± 10.8
0.336
Neutral
Varus and valgus
p Value
Level A
76.7 ± 11.1
72.8 ± 10.5
0.104
Level B
83.8 ± 10.5
75.5 ± 9.2
