A.G. Marsh

The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement

UNLABELLEDnWhen performing total knee replacement (TKR), surgeons are required to decide on the most appropriate size of tibial component. As implants are predominantly selected from incremental sizes of a preferred design, it may be necessary for a surgeon to slightly under or oversize the component. There are concerns that overhang could lead to pain from irritation of soft tissues, and an undersized component could lead to subsidence and failure. Patient reported outcome measures were recorded in 154 TKRs at one year postoperatively (in 100 TKRs) and five years post-operatively (in 54 TKRs) in 138 patients. The Oxford Knee Score (OKS), WOMAC and SF-12 were recorded, and a composite pain score was derived from the OKS and WOMAC pain questions. Tibial component size and position were assessed on scaled radiographs and implants were grouped into anatomic sized tibial component (78 TKRs), undersized component (48 TKRs), minor overhang one to three mm (10 TKRs) or major overhang ≥ 3 mm (18 TKRs). There was no statistically significant difference between the mean post-operative OKS, WOMAC, SF-12 or composite pain score of each group. Furthermore, localisation of the site of pain did not correlate with medial or lateral overhang of the tibial component. Our results suggest that tibial component overhang or undersizing is not detrimental to outcome measures or pain.nnnLEVEL OF EVIDENCEnII.

Total Hip Replacement in Developmental Dysplasia of the Hip Using Wagner Cone Prosthesis with Small Diameter Metal-On-Metal Articulation

Background nPatients with developmental dysplasia of hip often undergo total hip arthroplasty (THA) at a younger age. THA in such patients are technically demanding because of deficient acetabular bone stock, abnormal femoral anatomy with increased anteversion, leg length discrepancy and soft tissue imbalance. Conical femoral stem with Metal on Metal (MoM) 28 mm bearing have been used to address the anatomical and wear issues in this young patient group. The aim of the study was to review the early midterm clinical results of this prosthesis. nMaterial & Methods nBetween January 2004 and March 2009 twenty-one consecutive patients (24 hips) with osteoarthritis secondary to developmental dysplasia of the hip underwent metal-on-metal uncemented Allofit Metasul press-fit cups (Zimmer) with 28 mm-heads and tapered uncemented Wagner cone prosthesis stems (Zimmer) using posterior approach. nFunctional outcomes were assessed using Oxford hip score (OHS), SF12 physical and mental scores and WOMAC scores. Radiographic outcomes was carried out by two independent observers for leg length discrepancy (LLD), Crowe and Tonnis grading, lateral center -edge (CE) angle, acetabular roof-arc angle and femur neck-shaft angle heterotropic ossification, prosthesis loosening and cup inclination angle. nResults nThere were 5 men and 16 women with mean age of 45 years (SD=9.15, 26-63). The mean follow up was four years (SD=1.7, 2-7). No patients were lost to follow up. Three patients required structural allograft, no patients required intra operative femoral shortening. Classification of DDH was Crowe type I in 14 hips, type II in 8 hips and type III in 2 hips. The mean preoperative CE angle was 10.5°, neck shaft angle was 143° and the acetabular roof arc angle was 25°. 3 hips had Tonnis Grade 2 while 21 had Grade 3 osteoarthritis. The mean cup inclination angle was 42 degrees (range 32-60 degrees). The mean preoperative limb shortening was 19.1 mm (range,-1 to -39) which improved to 2.8 mm postoperatively. nThe OHS improved significantly within subjects (p<0.001) from a mean of 10.6 (2-28) to 43.9 (30-48). The mean post operative scores were- WOMAC 51 (SD=7.4, 30-56), SF12 physical 51 (SD=8.5, 28-58) and SF12 mental 53 (SD=4.7, 46-59). There were two revisions for aseptic loosening, one stem and one cup; therefore giving an overall survival of 91%. No other hip had radiographic evidence of acetabular or femoral osteolysis. Three patients suffered transient femoral nerve palsy, which recovered completely. We did not observe any dislocation, deep infection or heterotopic ossification. nDiscussion nThe medium-term results of the small diameter metal-on-metal hip arthroplasty with a conical uncemented stem have been encouraging in the treatment of this difficult cohort of young patients. The inherent stability and functional outcome provided by the small femoral heads are better than the recent large metal on metal articulations. Further follow up is required to see how small MoM bearing will behave in the long term.

Can we predict which dysplastic hips will require acetabular augmentation during total hip arthroplasty based on pre-operative radiographs?

Aims The purpose of this study was to evaluate whether an innovative templating technique could predict the need for acetabular augmentation during primary total hip arthroplasty for patients with dysplastic hips. Patients and Methods We developed a simple templating technique to estimate acetabular component coverage at total hip arthroplasty, the True Cup: False Cup (TC:FC) ratio. We reviewed all patients with dysplastic hips who underwent primary total hip arthroplasty between 2005 and 2012. Traditional radiological methods of assessing the degree of acetabular dysplasia (Sharps angle, Tönnis angle, centre‐edge angle) as well as the TC:FC ratio were measured from the pre‐operative radiographs. A comparison of augmented and non‐augmented hips was undertaken to determine any difference in pre‐operative radiological indices between the two cohorts. The intra‐ and inter‐observer reliability for all radiological indices used in the study were also calculated. Results Of the 128 cases reviewed, 33 (26%) needed acetabular augmentation. We found no difference in the median Sharps angle (p = 0.10), Tönnis angle (p = 0.28), or centre‐edge angle (p = 0.07) between the two groups. A lower TC:FC ratio was observed in the augmented group compared with the non‐augmented group (median = 0.66 versus 0.88, p < 0.001). Intra‐observer reliability was found to be high for all radiological indices analysed (interclass correlation coefficient (ICC) > 0.7). However, inter‐observer reliability was more variable and was only high for the TC: FC ratio (ICC > 0.7). Conclusion The TC: FC ratio gives an accurate estimate of acetabular component coverage. It can help predict which dysplastic hips are likely to need acetabular augmentation at primary total hip arthroplasty. It has high intra‐ and inter‐observer reliability.

Use of the trochanteric flip osteotomy to facilitate internal fixation of a femoral head fracture.

We report the case of a 42-year-old male who suffered a fracture–dislocation of the femoral head. After a closed reduction of the hip, this proceeded to an open reduction with internal fixation of the fractured femoral head, in addition to labral repair and micro-fracture of an articular cartilage defect. After considering the risks to the femoral head blood supply, the trochanteric flip osteotomy was used. This provided ample and safe exposure. At 14 months follow-up, the patient-reported outcome measures are favourable: modified Harris Hip Score (81/100), the non-arthritic hip score (92.5/100) and SF-12 (41/48).