The purpose of the study is to evaluate the retrospective results of 92 surgically treated spastic hips. Twenty-one patients were able to walk in the community with aids, 19 were able to walk about the house, and 13 were wheelchair bound. The mean age at the time of the operation was 7 yrs (3–18) and the average follow-up was 5. The cohort of the study included 45 tetraplegic patients, 6 diplegic, and 2 hemiplegic. The dislocated hips were 25 and the subluxated ones 67.

The surgical treatment included soft tissue and bone procedures. The 53 patients were divided into two age groups: those less than 7yrs old and those older than 7yrs. The cohort was also divided into 39 patients operated in one setting, and 14 operated in more than one. Clinical evaluation was based on the joint range of motion, the ambulatory status and the pain. The radiological evaluation criteria were based on Reimer's migration index, the center-edge angle, Sharp's angle, and neck-femoral angle. We used the interclass correlation coefficient to measure our interobserver reliability for MI 0,93, for CE angle 0,95 and for Sharp's angle 0,81, as the interobserver difference for MI averaged 9% for CE angle 7and for Sharp's angle 3.

Statistical analysis of continuous variables was done by Student's t-test or the Wilcoxon rank sum test. Categorical variables were evaluated by Fisher's test. Concerning the walking ability, from the 13 severe quadriplegic patients, none improved his functional level but they achieved better sitting balance. The walking ability of the rest of the patients improved one level in 78% of the cases. The mean preoperative abduction was improved from 24,7 to 33,5, the mean flexion was slightly reduced from 123 preoperatively to 114 postoperatively and the mean extension reduced from −20 preoperatively to −8 postoperatively. Reimer's index reduced from 67,2 to 21,7 postoperatively, the CE angle increased from −10,6 to 20,5, the Sharp's angle increased from 36,9 to 40,5 and the neck-shaft angle increased from 119,7 to 157,5post-operatively. Of greater significance were MI and CE at p<0.05. A migration index of >50% at final follow-up was associated with a worse migration index and a worse CE angle at 1 year post-operatively. 46 hips were evaluated as good, 30 as satisfactory, and 16 as poor. The severe tetraplegic with small-negative CE angle and Reimer's migration index > 50%, as well as the small age of the patients (<7 yrs) were negative prognostic factors. Better results were observed when patients were operated at age <7yrs by soft tissue procedures and MI<30%, while patients >7yrs had satisfactory results only after combined bony and soft tissue procedures and MI <50%. A migration index of >50% at final follow-up was associated with a worse migration index and a worse CE angle at 1 year postoperatively.

INTRODUCTION. Cementless Total Hip Replacement surgery is a well established procedure for relative young patients with severe hip disease. Excellent long term clinical results have been published on the performance of the femoral component. With growing clinical experience, our concern focused on excessive wear of the Ultra High Molecular Weight Polyethylene (UHMWPE) ringloc liner of the Mallory Head cementless Total Hip Prosthesis. After its introduction in our clinic in 1997, this implant is still in use without any modification. We were concerned that due to premature liner wear, the performance of this implant would not be compliant with the international guideline on implant survival (NICE guidelines: at 10 year follow up, 90% of all implants should still be in situ). Our objective was to establish the amount of liner wear in our first 200 MH implants. METHODS. Our first 200 patients consecutively treated with Mallory Head prostheses were followed up to obtain a recent digital image. Follow up was complete for 181 (90.5%) of our 200 patients. Ten had died and nine were not able or willing to come for follow up. The mean duration of follow up was 8.3 years (range: 8–13). The 181 recent digital images were classified as either excessive wear or no excessive wear by two independent orthopedic surgeons. Next, liner wear was measured in the 2D frontal plane using PolyWare Pro/3D Digital Version Rev 5.1 software (Draftware Developers, Conway, USA). A threshold for excessive liner wear was set at 0.2mm/year, according to literature. RESULTS. Using software for measuring PE wear, 46.7% of all patients had excessive UHMWPE wear (> 0.2mm/yr). There was no relation between the amount of wear and BMI, gender, component size or the acetabular inclination angle. Thirteen patients (6.5%) were revised. Nine of these revisions were for excessive liner wear or aseptic loosening (4.5%). For now, our series of cementless Mallory Head prostheses is compliant with the NICE guideline on implant survival. However, with the measured amount of wear we expect to see a significant increase in the number of revisions for liner wear in the near future. DISCUSSION. Our clinical observation of premature UHMWPE wear proved correct. The measured amount of UHMWPE wear is consistent with the few other studies published on this subject. Although we present a retrospective study, limiting the strength of our results, we have included a large group of patients with acceptable loss to follow up. It is unclear if the observed wear will lead to a sharp increase in the number of revisions within the next few years. Possibly, future revisions will be complicated by loss of acetabular bone stock following the pathofysiological reaction to wear particles. Our results can probably be generalised for any district hospital