Isolated popliteus tendon injury does not lead to abnormal laxity in posterior-stabilised total knee arthroplasty

PURPOSE

The popliteus tendon is crucial to postero-lateral stability and prone to iatrogenic injury intra-operatively. Its role in the stability of the replaced knee remains contentious. The aim of this study was to use computer navigation to quantify the effect of popliteus sectioning on the 'envelope of laxity' (EoL) offered by a posterior-stabilised (PS) total knee arthroplasty (TKA) and compare with that of the native knee.

METHODS

Loaded cadaveric legs were mounted on a purpose built rig. EoL was measured in 3 degrees of freedom using computer navigation. Knees were subjectively stressed in varus/valgus, internal/external rotation and anterior draw. This was performed preoperatively, during TKA and after sectioning of the popliteus tendon. Real-time data were recorded at 0°, 30°, 60° and 90° of flexion as the operating surgeon stressed the knee in 3 degrees of freedom to its subjective endpoint. Mixed-effect modelling was used to quantify the effects of intervention on degree of laxity.

RESULTS

In all conditions, there was an increase in laxity with knee flexion. Insertion of a PS TKA resulted in increased constraint, particularly in rotation. Sectioning of the popliteus did not result in a significant increase in knee laxity to 90º of knee flexion. However, at deeper flexion angles, tendon sectioning overcame the constraints of the implant resulting in a significant increase in rotatory and varus/valgus laxity towards the native condition.

CONCLUSION

These findings support the view that certain current designs of PS knee replacement can constrain the knee in flexion in the absence of postero-lateral deficiency. For this implant, isolated sectioning of the popliteus tendon did not substantially generate abnormal knee laxity.

Can we define envelope of laxity during navigated knee arthroplasty?

PURPOSE

Functional outcomes after knee arthroplasty (TKA) remain poor. The ability to restore the soft tissue envelope intraoperatively may improve such outcomes. The aim of this study was to extend the scope of computer navigation as a tool to quantifying the envelope of laxity during subjective stress testing preoperatively and to quantify the effects of knee replacement and how it changes as a result of ligamentous failure.

METHODS

Loaded cadaveric legs were mounted on a purpose-built rig. Envelope of laxity was measured in 3 degrees of freedom using computer navigation. Knees were subjectively stressed in varus/valgus, internal/external rotation and anterior draw. This was performed preoperatively, during TKA and after sequential sectioning of ligaments. Real-time data were recorded at 0°, 30°, 60° and 90° of flexion. Mixed effect modelling was used to quantify the effects of intervention on degree of laxity.

RESULTS

In all cases, there was an increase in laxity with increasing flexion or ligament sectioning. Operator and movement cycle had no effect. Insertion of a TKA showed increased stability within the joint, especially in internal/external rotation and anterior drawer. Once the PCL and popliteus were cut, the implant only maintained some rotatory stability; thereafter, the soft tissue envelope failed.

CONCLUSIONS

This work has shown a novel way by which computer navigation can be used to analyse soft tissue behaviour during TKA beyond the coronal plane and throughout range of motion. Despite subjective stress testing, our results show reproducible patterns of soft tissue behaviour-in particular a wide range of mid-flexion excursion. It also quantifies the limits within which a cruciate-retaining TKR can maintain knee stability. This functionality may guide the surgeon in identifying and/or preventing soft tissue imbalances intra-operatively, improving functional results.

Hand washing rituals in trauma theatre: clean or dirty?

INTRODUCTION

The aim of this study was to investigate the degree of contamination of a surgeon's hand following use of chlorhexidine gluconate or alcohol gel as disinfectants.

MATERIALS AND METHODS

In this prospective, randomised trial, orthopaedic surgeons were allocated to one of two different hand-washing protocols using a randomisation table. The hand-washing protocol dictated that all surgeons should wash for 5 min with chlorhexidine for their first case. Thereafter, the surgeon was randomised to wash for 3 min with either alcohol gel or chlorhexidine. At the end of each procedure, the gloves of each surgeon were carefully removed and the fingertips from each hand were placed on an agar plate. The number of bacterial colonies present after 24 h and 48 h of incubation were recorded for each agar plate by a microbiologist blinded to the washing protocol used.

RESULTS

Overall, 41 procedures and 82 episodes of hand washings were included in the study. Two episodes were discarded due to contamination at the time of glove removal. Four hands (8%) were contaminated in the chlorhexidine group compared to 19 (34%) in the alcohol group. Fisher's exact test confirmed a significantly higher risk of contamination using alcohol gel compared to chlorhexidine (P = 0.002). In addition, the average bacterial colony count was substantially higher in the alcohol group (20 colony forming units) compared to the chlorhexidine group (5 colony forming units). There was no relationship between the duration of surgery and the degree of contamination (P = 1.12).

CONCLUSIONS

Alcohol gel disinfectant is not a suitable alternative to chlorhexidine when hand washing before surgery. This study has identified a higher risk of bacterial contamination of surgeons' hands washed with alcohol. This may lead to higher levels of postoperative infection in the event of glove perforation.

Carpal tunnel syndrome: the correlation between outcome, symptoms and nerve conduction study findings

A retrospective study was performed on 62 patients who had undergone carpal tunnel decompression surgery. Each patient was assessed in clinic, their case notes were reviewed and their electrophysiological results were analysed and graded according to severity. The median preoperative duration of symptoms was 2 years. No relationship was found between the nature or duration of pre-operative symptoms and the severity of the electrophysiological impairment. Furthermore, no relationship could be identified between pre-operative nerve conduction impairment and either successful outcome of surgery (defined as complete symptom relief) or time to resolution of symptoms after surgery.

Tourniquet-induced wound hypoxia after total knee replacement

We have investigated whether the thigh tourniquet used during total knee replacement (TKR) influenced the development of postoperative wound hypoxia and was a cause of delayed wound healing. We allocated randomly 31 patients (31 TKRs) to one of three groups: 1) no tourniquet; 2) tourniquet inflated at low pressure (about 225 mmHg); and 3) tourniquet inflated to high pressure of about 350 mmHg. Wound oxygenation was measured using transcutaneous oxygen electrodes. In the first week after surgery, patients with a tourniquet inflated to a high pressure had greater wound hypoxia than those with a low pressure. Those without a tourniquet also had wound hypoxia, but the degree and duration were less pronounced than in either of the groups with a tourniquet. Use of a tourniquet during TKR can increase postoperative wound hypoxia, especially when inflated to high pressures. Our findings may be relevant to wound healing and the development of wound infection.

Tourniquet-induced wound hypoxia after total knee replacement

We have investigated whether the thigh tourniquet used during total knee replacement (TKR) influenced the development of postoperative wound hypoxia and was a cause of delayed wound healing.

We allocated randomly 31 patients (31 TKRs) to one of three groups: 1) no tourniquet; 2) tourniquet inflated at low pressure (about 225 mmHg); and 3) tourniquet inflated to high pressure of about 350 mmHg. Wound oxygenation was measured using transcutaneous oxygen electrodes.

In the first week after surgery, patients with a tourniquet inflated to a high pressure had greater wound hypoxia than those with a low pressure. Those without a tourniquet also had wound hypoxia, but the degree and duration were less pronounced than in either of the groups with a tourniquet.

Use of a tourniquet during TKR can increase postoperative wound hypoxia, especially when inflated to high pressures. Our findings may be relevant to wound healing and the development of wound infection.

Risk factors for pre-eclampsia among Zimbabwean women: maternal arm circumference and other anthropometric measures of obesity

Maternal pre-pregnancy obesity is a risk factor for pre-eclampsia (proteinuric hypertension in pregnancy) among North American and European women. We studied the relationship between maternal obesity and risk of pre-eclampsia among Zimbabwean women. A case-control study was conducted at Harare Maternity Hospital, Harare, Zimbabwe, between June 1995 and April 1996. Study participants were 144 women with pre-eclampsia and 194 normotensive women serving as controls. Maternal weight, height and mid-arm circumference were measured and recorded during study participants' postpartum hospital admission. Maternal mid-arm circumference, considered to be relatively stable during pregnancy among women of developing countries, was used as the primary indicator of maternal pre-pregnancy obesity. Logistic regression procedures were used to estimate odds ratios and 95% confidence intervals. There were linear trends in risk of pre-eclampsia with increasing mid-arm circumference, increasing weight and increasing body mass index. After adjusting for potential confounding factors, women in the highest quintile for mid-arm circumference (28-39 cm) were 4.4 times more likely to have had their pregnancy complicated by pre-eclampsia than women in the lowest quintile (21-23 cm). Odds ratios of similar magnitude were observed for the other anthropometric measures. To our knowledge, this is the first study to demonstrate a positive association between maternal obesity and pre-eclampsia risk in a black African population. Biological mechanisms thought to explain this relatively consistent epidemiological finding include endothelial cell injury, possibly resulting from hyperlipidaemia.