M. Hassaballa

Does the joint line matter in revision total knee replacement

We identified 148 patients who had undergone a revision total knee replacement using a single implant system between 1990 and 2000. Of these 18 patients had died, six had developed a peri-prosthetic fracture and ten had incomplete records or radiographs. This left 114 with prospectively-collected radiographs and Bristol knee scores available for study. The height of the joint line before and after revision total knee replacement was measured and classified as either restored to within 5 mm of the pre-operative height or elevated if it was positioned more than 5 mm above the pre-operative height. The joint line was elevated in 41 knees (36%) and restored in 73 (64%). Revision surgery significantly improved the mean Bristol knee score from 41.1 (SD 15.9) pre-operatively to 80.5 (SD 15) post-operatively (p < 0.001). At one year post-operatively both the total Bristol knee score and its functional component were significantly better in the restored group than in the elevated group (p < 0.01). Overall, revision from a unicondylar knee replacement required less use of bone graft, fewer component augments, restored the joint line more often and gave a significantly better total Bristol knee score (p < 0.02) and functional score (p < 0.01) than revision from total knee replacement. Our findings show that restoration of the joint line at revision total knee replacement gives a significantly better result than leaving it unrestored by more than 5 mm. We recommend the greater use of distal femoral augments to help to achieve this goal.

Observed kneeling ability after total, unicompartmental and patellofemoral knee arthroplasty: perception versus reality.

Kneeling is an important function of the knee, but little information is available on ability to kneel after different knee arthroplasty procedures. Previous work has asked patients about their kneeling ability; in this study it was objectively assessed. One hundred and twenty two patients — 38 having had total knee replacement (TKR), 53 unicompartmental knee replacement (UKR), 31 patello-femoral replacement (PFR) — were observed trying to kneel at 90° on a chair, at 90° on the floor, and at 120° on the floor. Only 37% of patients thought they could kneel, whereas 81% were actually able to kneel (p <0.001). Ability to kneel on the chair and on the floor at 90°was significantly better than perceived ability for all prosthesis types (p <0.001). Kneeling at 120° showed no difference between perception and reality except for the PFR group (p <0.05). In all positions, increased range of movement significantly improved kneeling ability (p <0.001). Kneeling ability in men was significantly better than in women (p <0.001). Patient-centred questionnaires do not accurately document kneeling ability after knee arthroplasty.

Subsidence of the stem after impaction bone grafting for revision hip replacement using irradiated bone

Loss of bone stock is a major problem in revision surgery of the hip. Impaction bone grafting of the femur is frequently used when dealing with deficient bone stock. In this retrospective study a consecutive series of 68 patients (69 hips) who had revision of a hip replacement with femoral impaction grafting were reviewed. Irradiated bone allograft was used in all hips. Radiological measurement of subsidence of the stem, incorporation of the graft and remodelling was carried out and showed incorporation of the graft in 26 of 69 hips (38%). However, there was no evidence of trabecular remodelling. Moderate subsidence of 5 mm to 10 mm occurred in ten hips (14.5%), and massive subsidence of > 10 mm in five (7.2%). The results of this study are less favourable than those of others describing studies of revision of the femoral stem using impaction bone grafting. The absence of the characteristic changes of graft remodelling noted in other series raises the question as to whether irradiated bone graft may be a significant factor influencing the post-operative outcome.

The Posterior Condylar Offset Ratio.

INTRODUCTION Posterior Condylar Offset is an area of interest in knee arthroplasty research and clinical outcome. The aim of the study is to define a quantifiable Posterior Condylar Offset Ratio, a normal value for this ratio and to confirm its reproducibility on pre-operative radiographs. METHOD We propose a new Posterior Condylar Offset Ratio which is defined as the maximal thickness of the posterior condyle projecting posteriorly to a straight line drawn as the extension of the posterior femoral shaft cortex, divided by the maximal thickness of the posterior condyle projecting posterior to a straight line drawn as the extension of the anterior femoral shaft cortex on a true lateral radiograph of the distal quarter of the femur. We have measured this on 100 true lateral radiographs (50 females, 50 males, and mean age 65 years). RESULTS The mean ratio was 0.44 (SD 0.02) and was shown to have good reproducibility (intra-observer error 0.899 and inter-observer error 0.882. The ratio was also very consistent between male and female patients (0.44 (SD 0.02) for the males and 0.45 (SD 0.02) for the females). Adjusting the ratio for reported posterior condyle articular cartilage thickness increased the ratio to 0.47 (SD 0.02). CONCLUSION We suggest our Posterior Condylar Offset Ratio is a useful tool to aid further research in this area of knee arthroplasty and propose a normal value of 0.44 on radiographs and 0.47 on post-operative knee arthroplasty radiographs.

Do long leg supine CT scanograms correlate with weight-bearing full-length radiographs to measure lower limb coronal alignment?

INTRODUCTION The gold standard for measuring knee alignment is the lower limb mechanical axis (MA) using weight-bearing lower limb full-length x-ray (FLX). However, CT scanograms (CTS) are becoming increasingly popular in view of lower radiation exposure, speed of data acquisition and supine positioning. We compared the correlation and degree of agreement of knee joint coronal alignment using these two imaging modalities. METHOD From our series of complex primary and revision knee arthroplasty patients, we selected those with both FLX and CTS recorded onto digital PACS. The coronal alignments were assessed in 24 knees and the valgus/varus angles relative to the MA were measured. Results were analysed statistically using the paired samples t-test, Pearsons correlation coefficient, intra-class correlation coefficient, Cohens kappa and Passing and Bablok regression to assess potential equality of methods. RESULTS The mean MA was 180.5° (165°-200°) for the CTS and 181° (164°-202°) for the FLX. The CTS MA angle data between the assessors were highly correlated (r=0.971, p <0.001) as were FLX MA angle measurements (r=0.988, p <0.001). 41.7% of the CTS and 37.5% of the FLX were in varus alignment, while 50% of the CTS and 43.8% of the FLX were in valgus alignment. Malalignment >5° was revealed by 18.8% of the CTS and 35.4% of the FLX. CONCLUSION Overall, good agreement was observed in MA angle data between the two imaging modalities, but reproducibility may be problematic. In the malaligned limb, weight-bearing FLX still remains a vital imaging modality. CTS should be used with caution in view of the under-detection of malalignment.

Kneeling requirements and arthroplasty surgery

We investigated the physical characteristics and symptoms related to kneeling in a normal population. One hundred people were recruited at random. Of these, 27 subjects had knee pain and 73 were normal. Measurements were in kilograms with subjects on scales in three positions: standing, kneeling at 90 degrees and kneeling at full flexion. All 73 normal subjects could kneel at 90 degrees with an average of 94% of their body weight and at full flexion with an average of 51% of their body weight. The 27 subjects with knee pain were able to kneel at 90 degrees with an average of 97% of their body weight and in full flexion with an average of 50% of their body weight. Weight transmitted through the knees at full flexion is significantly less than when at 90 degrees whether subjects had pain or not. Future development of knee arthroplasty, when catering for kneeling might need to concentrate on achieving a better range of movement.

Minimally invasive total knee arthroplasty; a pragmatic randomised controlled trial reporting outcomes up to 2 year follow up.

BACKGROUND We present a prospective, randomised, multi-surgeon, controlled trial comparing minimally invasive (MIS) and standard approach total knee arthroplasty (TKA). METHODS Participants underwent unilateral TKA. Patients were randomised to Bristol, quadriceps sparing MIS or standard medial parapatellar approaches. Length of stay with secondary outcome measures including knee range of movement, Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC) and American Knee Society Score (KSS) up to 2 years. Radiographic and post operative assessment was blinded. RESULTS 86 patients (92 knees) participated in the study. Mean operative time between MIS and control groups was 95.5 (95% CI 90.0-101.0) and 94.8 (95% CI 88.2-101.4) minutes respectively. Mean readiness for discharge was shorter in the MIS group 4.5±1.5 (95% CI, 4.1-4.9) days versus 5.9±2.7 (95% CI, 5.1-6.7) days amongst controls (p=0.004). Patients in the MIS group had fewer complications (p=0.003). One patient developed a deep vein thrombosis (DVT) and one required revision surgery, both in the control group. 83 patients completed follow up to 2 years (40 MIS, 43 controls). Range of movement and other outcome measures improved up to 1 year post-operatively with no statistically significant differences between MIS and controls. We found no evidence of radiographic loosening in either group at the 2 year follow up. CONCLUSIONS MIS offers reduced length of stay and fewer complications for patients following TKR without evidence of component mal-alignment. Our findings of fewer systemic complications in MIS TKR patients warrant further future study. LEVEL OF EVIDENCE Level 1.

The Journey patellofemoral joint arthroplasty: A minimum 5 year follow-up study

BACKGROUND The Journey patellofemoral joint arthroplasty (PFA) was designed to improve patient outcomes following surgical management of patellofemoral joint osteoarthritis. It is based on the asymmetric trochlear geometry of the Genesis II total knee arthroplasty, with Oxinium components, to provide a reliable treatment option in an often young, high demand group of patients. METHODS We report the minimum five year functional outcome and survivorship of the Journey PFA performed at our institution between October 2005 and September 2009. RESULTS A total of 101 Journey PFAs were implanted in 83 patients, and we have complete outcomes for 90 implants (89%). There were 80 implants in female patients, and the mean age at time of surgery was 60years (26 to 86). The median Oxford Knee Score (0 to 48) improved from 18 to 30, and median Western Ontario and McMaster University Osteoarthritis Short Form Index (0 to 60) improved from 22 to 35. There were a total of 12 revisions, with mean time to revision 50months (10 to 99). CONCLUSIONS The Journey PFA gives a good medium-term functional outcome with 88% survivorship at a mean of seven years. This is the largest study of Journey PFA in the literature, and it provides a reliable option for patients with isolated patellofemoral joint osteoarthritis when arthroplasty is considered.

Iatrogenic surface damage during femoral component impaction in total knee arthroplasty.

Application of prosthesis components during knee arthroplasty surgery involves impacting the femoral component using an impaction device and a heavy mallet. This could damage the component and may therefore be of concern to knee surgeons. Using a drop tower with a set-up that mimics the impaction generated clinically when a surgeon hits the femoral component, we investigated the possible surface damage to the femoral component. Three parameters were obtained and compared with a contact profilometer to characterize the roughness: R(a), R(pk) and R(z). The effect of the impacts on the contour of the femoral components was also investigated. After 3 series of impactions, no difference in surface roughness of the femoral component important enough to increase the wear rate could be detected neither for Cobalt Chrome or Oxidized Zirconium components. Our study therefore indicates that impacting the femoral component during TKA does not alter the components surface roughness.