N. Fouilleron

Component impingement in total hip arthroplasty: Frequency and risk factors. A continuous retrieval analysis series of 416 cup

INTRODUCTION Impingement is a factor of failure in total hip replacement (THR), causing instability and early wear. Its true frequency is not known; cup-retrieval series reported rates varying from 27 to 84%. HYPOTHESIS The hypothesis was that a large continuous series of THR cup removals would help determine the frequency of component impingement. OBJECTIVES The hypothesis was tested on a continuous retrospective series of cups removed in a single center, with a secondary objective of identifying risk factors. MATERIAL AND METHODS [corrected] Macroscopic examination looked for component impingement signs in 416 cups retrieved by a single operator between 1989 and 2004. Risk factors were investigated by uni- and multivariate analyses in the 311 cases for which there were complete demographic data. In these 311 cases, removal was for aseptic loosening (131 cases), infection (43 cases), instability (56 cases), osteolysis (28 cases) or unexplained pain (48 cases); impingement was explicitly implicated in only five cases (1.6%), always with hard-on-hard bearing components. RESULTS Impingement was found in 214 of the 416 cups (51.4%) and was severe (notch>1mm) in 130 (31.3%). In the subpopulation of 311 cups, impingement was found in 184 cases (59.2%) and was severe in 109 (35%). Neither duration of implant use nor cup diameter or frontal orientation emerged as risk factors. On univariate analysis, impingement was more frequently associated with revision for instability, young patient age at THR, global hip range of motion >200° or use of an extended femoral head flange (or of an elevated antidislocation rim liner), and was more severe in case of head/neck ratio<2. On multivariate analysis, only use of an extended head flange (RR 3.2) and revision for instability (RR 4.2) remained as independent risk factors for impingement. DISCUSSION Component impingement is frequently observed in cups after removal, but is rarely found as a direct indication for revision, except in case of hard-on-hard friction couples (polyethylene being the most impingement-tolerant material). Systematic use of extended head flanges and elevated antidislocation rims is not to be recommended, especially in case of excessive ROM. A good head/neck ratio should be sought, notably by increasing the head diameter in less impingement-tolerant hard-on-hard friction couples. Although not identified as a risk factor in the present study, implant orientation should be checked; computer-assisted surgery can be useful in this regard, for adaptation to the patients individual range-of-motion cone.

Proximal tibial derotation osteotomy for torsional tibial deformities generating patello-femoral disorders

INTRODUCTION Torsional abnormalities of the leg may cause instability and pain in the patellofemoral joint. Although derotation osteotomies seem logical to address these conditions, there are very few surgical results reported in the literature. HYPOTHESIS Isolated tibial derotation osteotomies relieve patellofemoral pain and instability even in the event of combined femoral and tibial torsion abnormalities. AIM Test this hypothesis in a retrospective and continuous series of thirty-six tibial derotation osteotomies and define the factors of success and failure. PATIENTS AND METHODS Thirty-six derotation osteotomies of the proximal tibial metaphysis were performed between 1995 and 2006 in 29 patients (five men and 24 women, an average of 26.5 years old±7.4 (18-44)) followed-up for a mean 4.7 years. There was confirmed patellar instability in five knees, and patellofemoral pain without instability in 31. A proximal metaphyseal osteotomy was performed to correct excessive external tibial rotation as well as to recenter the tibial tubercle after anterior tibial cortex elevation. All patients were followed-up and the clinical data were analysed according to criteria from the Lille score [specifically designed for patellofemoral joints (100 point score)] and the IKS score. All patients had a preoperative radiological evaluation [(including measurement of torsion abnormalities in 32 cases by computed tomodensitometry (CT scan))]. The mean preoperative external tibial torsion measured on CT scan was 36.2°±9.48 (26-51°) and the mean femoral anteversion was 19.4°±9.5 (8-36°). RESULTS Twenty-seven patients (94%) were satisfied or very satisfied. The Lille score increased from 54.8±16.9 (30-92) preoperatively to 85.2±14.2 (36-100) at follow-up. The mean IKS knee scores and function increased from 56±14.8 (45-94) to 94±12.1 (60-100) and from 71±18.4 (30-100)-96±11.9 (50-100). Patellofemoral dislocations did not occur in any of the five cases with instability. Mean derotation was 25° measured with a mean tibial torsion measured clinically at follow-up 8.6°±7.2 (0-30). Two reoperations were necessary, (one knee manipulation under general anesthesia, and in another the fibular fibrous arch had to be released). One case of regressive palsy of the common fibular nerve was observed. Union of the osteotomy was obtained in all patients. DISCUSSION This series is one of the largest series published to date. Isolated medialization of the anterior tibial tubercle only partially corrects these morphological abnormalities. In cases of associated excessive femoral anteversion we recommend surgery to the tibia alone because results were comparable in groups with and without excessive anteversion of the femoral neck. LEVEL OF EVIDENCE level IV. Retrospective study.

Poor short-term outcomes after computer-assisted rotating-platform total knee arthroplasty with a deep-trochlear-groove femoral component: analysis of 19 patients.

BACKGROUND Congruent rotating tibial plateaus are designed to minimise wear after total knee arthroplasty (TKA). The Score™ prosthesis has a congruent rotating tibial plateau, a deep trochlear groove, and uses a computer-assisted navigation system for ligament balancing. Although this prosthesis is widely utilized, no accurate data on outcomes are available. HYPOTHESIS The innovative features of the Score™ prosthesis, most notably patellar replacement with a highly constrained femoral component, do not jeopardize implant survival. PATIENTS AND METHODS In a pilot study, we retrospectively evaluated outcomes of 19 patients treated with Score™ knee replacement between February and October 2006 (mean age, 66.8 years; range, 58-82 years). The evaluation criteria were the International Knee Society (IKS) scores and prosthesis survival rate estimated using Kaplan-Meier plots with failure defined as revision need to change the prosthesis. RESULTS Mean follow-up was 35.3 months. The IKS knee score increased from 27.4 (5-60) preoperatively to 81.4 (45-99) at last follow-up (P<0.0001). Mean mechanical axis was 181.2° (180-186°), with 16 between 180° and 183°. Revision surgery was required in five cases (for patellar complications with combined motion-range limitation in flexion (<90°) and extension (5-20°) in three cases, isolated motion-range limitation in one case, and recurvatum deformity with instability in one case). Prosthesis survival was 82% (73-91%) after 24 months and 65% (51-78%) after 44 months. DISCUSSION The deep trochlear groove femoral component resulted in patellar complications, which were the most common reasons for revision surgery, together with motion-range limitation and instability possibly related to improper use of the navigation system. This small retrospective case-series study showed an unusually low prosthesis survival rate probably related to the implant design. We no longer use the Score™ prosthesis, despite the availability of a dedicated navigation system, and we recommend careful monitoring of patients who have this prosthesis. LEVEL OF EVIDENCE Level IV, retrospective study.