Damien Bennett

Comparison of early postoperative functional levels following total hip replacement using minimally invasive versus standard incisions. A prospective randomized blinded trial

Objective: To compare the results of single-incision minimally invasive total hip replacement (≤ 10 cm) to standard-incision (16 cm) total hip replacement in the early postoperative period with respect to functional and mobilizing ability (transfers, mobilizing, walking and stair assessment). Setting: Orthopaedic wards of a regional orthopaedic centre. Subjects: Two hundred and nineteen total hip replacement patients were tested between December 2003 and June 2004. Interventions: Patients were randomized to either total hip replacement through a minimally invasive (≤ 10 cm) or standard incision (16 cm). A single surgeon performed all procedures using the same type of component fixation. Postoperative physiotherapy assessment and treatment was standardized. Analgesia was also standardized. All patients, physiotherapy staff and assessors were blinded to the incision used. Main outcome measures: Patients were tested two days post operatively and were assessed for the following activities: transfer from supine to sit, transfer from sitting to standing, mobilizing, ascending and descending stairs and weight-bearing. Results: The shorter incision offered no significant improvement in patient ability in relation to transfer from lying to sitting, transfer from sitting to standing, mobilizing or weight-bearing. Ascending/descending stairs gave a total time for the minimal incision of 38.7 s against 40.8 s for a standard incision. There was no difference in walking velocity between the standard incision and minimal incision groups two days post operatively (minimal incision = 0.26 m/s versus standard incision = 0.26 m/s) or six weeks post operatively (minimal incision = 0.90 m/s versus standard incision = 0.93 m/s). There was no difference between groups with respect to walking aids at six-week review. The mean length of stay for the minimally invasive approach was 3.65 days (SD 2.04) against 3.68 days (SD 2.45) for the standard approach. This was not significantly different. Conclusion: Total hip replacement performed through a minimally invasive incision of ≤ 10 cm compared with a standard incision of 16 cm offers no significant benefit in terms of the rate or ability of patients to mobilize and perform functional tasks necessary for safe discharge.

Gait kinematics of age-stratified hip replacement patients—A large scale, long-term follow-up study

Three-dimensional gait analysis data from 134 patients attending routine 10-year post-operative review clinics is presented. Patients were divided into five age groups-54-64 years, 65-69 years, 70-74 years, 75-79 years and over 80 years. A group of 10 normal elderly subjects was also tested. All age groups displayed reduced range of hip flexion/extension, range of knee flexion extension, maximum hip extension and range of hip abduction/adduction and reduced velocity and step length compared to the normal elderly group. However, there was no difference in gait kinematics between the age groups. Patients over 80 years of age displayed significantly reduced range of sagittal plane ankle motion, but this is unlikely to be secondary to hip joint restriction and more likely due to reduced walking speed associated with very elderly subjects. This study reveals that even the youngest hip replacement patients do not attain normal gait kinematics 10-year post-operatively and that muscle atrophy and residual stiffness may influence patient kinematics many years post-operation.

Comparison of hip and knee arthroplasty outcomes at early and intermediate follow-up.

A common perception among clinicians and patients is that recovery is similar following total hip arthroplasty (THA) and total knee arthroplasty (TKA). Improvement in the outcomes of 337 THAs and 256 TKAs implanted by the same surgeon between April 2003 and November 2005 were compared. Improvement was measured using changes in Oxford hip and knee scores measured preoperatively, at first follow-up, and 1 year postoperatively for each patient. Improvements between preoperative review and first follow-up and between preoperative review and 1-year postoperative follow-up were significantly greater for THA compared to TKA patients. Improvements between first postoperative follow-up and 1-year postoperative follow-up were not significantly different between THA and TKA patients. Although THA patients displayed a significantly worse score preoperatively, they displayed a significantly better score at both first follow-up and 1-year postoperative follow-up. While both procedures improve postoperative pain and physical function, as measured by the Oxford score, improvements measured relative to preoperative levels were significantly smaller for TKA compared to THA patients. Despite recent advances in knee arthroplasty surgery, a significant proportion of TKA patients achieve relatively poor outcome scores postoperatively. This study shows that pain and function improve less and more slowly in the early and intermediate postoperative periods for knee compared to hip arthroplasty patients.

Wear paths produced by individual hip-replacement patients--a large-scale, long-term follow-up study.

Wear particle accumulation is one of the main contributors to osteolysis and implant failure in hip replacements. Altered kinematics produce significant differences in wear rates of hip replacements in simulator studies due to varying degrees of multidirectional motion. Gait analysis data from 153 hip-replacement patients 10-years post-operation were used to model two- and three-dimensional wear paths for each patient. Wear paths were quantified in two dimensions using aspect ratios and in three dimensions using the surface areas of the wear paths, with wear-path surface area correlating poorly with aspect ratio. The average aspect ratio of the patients wear paths was 3.97 (standard deviation=1.38), ranging from 2.13 to 10.86. Sixty percent of patients displayed aspect ratios between 2.50 and 3.99. However, 13% of patients displayed wear paths with aspect ratios >5.5, which indicates reduced multidirectional motion. The majority of total hip replacement (THR) patients display gait kinematics which produce multidirectional wear paths, but a significant minority display more linear paths.

Intra-operative and short term outcome of total knee arthroplasty in morbidly obese patients

BACKGROUND Longer operation times, poorer patient outcomes and increased early post-operative complications are reasons cited for not undertaking total knee arthroplasty (TKA) on morbidly obese patients. This study tests the hypothesis that there is no difference in intra-operative parameters between morbidly obese and non-obese patients, and no difference in patient outcome. METHODS Intra-operative parameters, post-operative complications, patient outcomes and knee range of motion were compared between morbidly obese patients (BMI>40 kg/m2) and individually age and gender matched non-obese patients (BMI<30 kg/m2) undergoing cementless rotating platform TKA. RESULTS Anaesthetic times and length of hospital stay were not significantly different between the morbidly obese and non-obese patients. Surgical time was significantly greater in morbidly obese patients. Improvements in patient outcomes following TKA were not significantly different between the morbidly obese and non-obese patients at early and short-term follow-up. CONCLUSIONS In contrast to previous studies, post-operative complication rates within three months of surgery and up to one year post-operatively were not significantly higher for morbidly obese patients. LEVEL OF EVIDENCE III.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates.

Variation in wear paths is known to greatly affect wear rates in vitro, with multidirectional paths producing much greater wear than unidirectional paths. This study investigated the relationship between multidirectional motion at the hip joint, as measured by aspect ratio, sliding distance, and wear rate for 164 hip replacements. Kinematic input from three‐dimensional gait analysis was used to determine the wear paths. Activity cycles were determined for a subgroup of 100 patients using a pedometer study, and the relationship between annual sliding distance and wear rate was analyzed. Poor correlations were found between both aspect ratio and sliding distance and wear rate for the larger group and between annual sliding distance and wear rate for the subgroup. However, patients who experienced a wear rate <0.08 mm/year showed a strong positive correlation between the combination of sliding distance, activity levels, and aspect ratio and wear rate (adjusted r2 = 55.4%). This group may represent those patients who experience conditions that most closely match those that prevail in simulator and laboratory tests. Although the shape of wear paths, their sliding distance, and the number of articulation cycles at the hip joint affect wear rates in simulator studies, this relationship was not seen in this clinical study. Other factors such as lubrication, loading conditions and roughness of the femoral head may influence the wear rate.

The influence of immediate knee flexion on blood loss and other parameters following total knee replacement

In an initial randomised controlled trial (RCT) we segregated 180 patients to one of two knee positions following total knee replacement (TKR): six hours of knee flexion using either a jig or knee extension. Outcome measures included post-operative blood loss, fall in haemoglobin, blood transfusion requirements, knee range of movement, limb swelling and functional scores. A second RCT consisted of 420 TKR patients randomised to one of three post-operative knee positions: flexion for three or six hours post-operatively, or knee extension. Positioning of the knee in flexion for six hours immediately after surgery significantly reduced blood loss (p = 0.002). There were no significant differences in post-operative range of movement, swelling, pain or outcome scores between the various knee positions in either study. Post-operative knee flexion may offer a simple and cost-effective way to reduce blood loss and transfusion requirements following TKR. We also report a cautionary note regarding the potential risks of prolonged knee flexion for more than six hours observed during clinical practice in the intervening period between the two trials, with 14 of 289 patients (4.7%) reporting lower limb sensory neuropathy at their three-month review.

The influence of shape and sliding distance of femoral head movement loci on the wear of acetabular cups in total hip arthroplasty

Abstract Wear of the polyethylene acetabular component is the most serious threat to the long-term success of total hip replacements (THRs). Greatly reduced wear rates have been reported for unidirectional, compared to multidirectional, articulation in vitro. This study considers the multidirectional motions experienced at the hip joint as described by movement loci of points on the femoral head for individual THR patients. A three-dimensional computer program determined the movement loci of selected points on the femoral head for THR patients and normal subjects using kinematic data obtained from gait analysis. The sizes and shapes of these loci were quantified by their sliding distances and aspect ratios with substantial differences exhibited between individual THR patients. The average sliding distances ranged from 10.0 to 18.1 mm and the average aspect ratios of the loci ranged from 2.5 to 9.2 for the THR patients. Positive correlations were found between wear rate and average sliding distance, the inverse of the average aspect ratio of the loci and the product of the average sliding distance and the inverse of the average aspect ratio of the loci. Patients with a normal hip joint range of motion produce multidirectional motion loci and tend to experience more wear than patients with more unidirectional motion loci. Differing patterns of multidirectional motion at the hip joint for individual THR patients may explain widely differing wear rates in vivo.

Activity Levels and Polyethylene Wear of Patients 10 years Post Hip Replacement

BACKGROUND Wear of the acetabular cup and implant loosening in total hip arthroplasty are thought to be affected by individual patient activity levels. METHODS Activity levels of 100 patients with unilateral primary hip replacements were measured using a digital pedometer 10-years post-operatively. FINDINGS Activity rates of hip replacement patients 10 years post surgery were found to fall with increasing age strata, with the age group 70-74 years showing significantly reduced activity rates compared to the 55-64 years age group and the age group greater than 80 years showing significantly reduced activity rates compared to both the 55-64 years age group and the 65-69 years age group. However, a clear correlation between age and activity was not found. Acetabular cup wear showed no relationship with patient activity levels. INTERPRETATION Progressive reduction in activity levels with more elderly hip replacement patients may inform long term planning of hip arthroplasty and implant choice.

A randomised controlled trial investigating the effect of posterior capsular stripping on knee flexion and range of motion in patients undergoing primary knee arthroplasty

Increasing knee flexion following total knee arthroplasty (TKA) has become an important outcome measure. Surgical technique is one factor that can influence knee motion. In this study, it was hypothesised that stripping of the posterior knee capsule could improve flexion and range of motion (ROM) following TKA. Patients who were undergoing TKA were prospectively randomised into two groups - one group (62 patients) were allocated stripping of the posterior knee capsule (PCS), the other group (66 patients) no stripping (no-PCS). The primary outcome was change in flexion and ROM compared to pre-operative measurements at three time points; after wound closure, 3 months and 1 year post-operatively. Secondary outcomes were absolute measurements of flexion, extension, ROM and complications. All operations were performed by a single surgeon using the same implant and technique. All patients received identical post-operative rehabilitation. There was a significant gain in flexion after wound closure in the PCS group (p=0.022), however there was no significant difference at 3 months or 1 year post-operatively. Absolute values of extension (p=0.008) and flexion (p=0.001) 3 months post-operatively were significantly reduced for the PCS group. The absolute value of ROM was significantly higher for the no-PCS group at 3 months (p=0.0002) and 1 year (p=0.005).There were no significant difference in the rate of complications. Posterior capsular stripping causes a transient increase in flexion that does not persist post-operatively. We do not recommend routine stripping of the posterior knee capsule in patients undergoing TKA.