For Surgeons

Introduction

Conventional approaches to hip resurfacing have disadvantages of their own. The average surgical incision is well in excess of 15cm. Prolonged rehabilitation, stiffness and heterotopic bone formation (2-3%) have also been reported in the literature. Minimally invasive surgical techniques for total hip arthroplasties have been described in the literature. This includes two incisions, mini posterior and a direct anterior approach. There have been no reports describing a minimally invasive approach for hip resurfacing. We describe a unique surgical approach for hip resurfacing and report the mid term results of a consecutive series of patients with minimally invasive hip resurfacing (MIHR^®).

Patients and Methods

Between December 2001 and February 2006, 136 hip resurfacings were performed by the author using the default technique. The essential criteria for MIHR were the unique surgical approach, dedicated MIS tissue retractor and specialised instruments for implant delivery. Specialised instruments included femoral neck targeting device, tissue protector, acetabular reamer and acetabular impactor. The author performed all the operations using a posterior approach. All patients were prospectively reviewed at 6 weeks, 3, 6 months and yearly thereafter. Patient age, sex and demographic data were collected from the medical notes. The clinical outcome was measured using Oxford Hip scores (OHS). The functional outcome was assessed using the Dartmouth COOP functional assessment chart. Following their final review, postal questionnaires elaborating the OHS and COOP charts were sent to all patients. The mean follow up was 26 months (6-68 months).

Results

The mean age of the patients was 56 years (range 30-78 yrs). Forty seven patients were male. Twelve patients had bilateral resurfacing arthroplasties. The average body mass index was 32 (17.5 to 41.7). The skin incision which was measured at the final review ranged from between 6 and 10cm with a mean of 7cm. The average blood loss was 245 ml (100-800ml). The mean Oxford hip score at final follow up was 17.9 (range 12-52). The mean COOP score at final review was 19.8 (9-36). Only one patient had an Oxford hip score of 52. She had undergone bilateral hip replacements (resurfacing -Rt, metal on metal arthroplasty - Lt). Post operatively she developed intractable bilateral trochanteric bursitis. Furthermore, she had severe cardiac co-morbidities which determined her poor scores. The final follow up radiograph at 5 years. There were no infections, dislocations, iatrogenic nerve injuries or heterotopic bone formation in this series of patients. Two patients had early fractures of the femoral neck at 4 and 6 weeks. They were successfully revised to a total hip replacement. The overall survival with revision for any cause as an end point at 3 years was 97.1 % (CI - 2.6%).

Discussion and Conclusion

There are no current reports in the literature describing a minimally invasive approach and the clinical results for MIHR. Our results show excellent clinical outcome comparable with other prostheses. This study shows that minimally invasive hip resurfacing can be carried out with excellent results. A longer follow up is needed to establish the longevity of the implants and the advantages of this approach.

Surgeons FAQ

Mini-incision surgery is a specialised technique performed by only a few talented surgeons. Is this the case for MIS?

Mr Chana: Even more so. However, my personal experience with the modified MIS posterior approach, training surgeons is quite easy if the surgeon is already carrying out more than 50 THA per year using the conventional posterior approach. These surgeons can be trained in three to four sessions. Surgeons using anterior or antero-lateral approaches would require a more lengthy training process due to the change in approach.

Mini-incision surgery has been around for a while, what makes MIS so important?

Mr Chana: Mini-incision usually implies an incision around 10-15cm and is usually a smaller incision of the conventional approach and should not be confused with minimally invasive surgery. The MIS incision may well be the 10cm part of the conventional incision but special instruments have to be used to allow the surgery to be carried out. However, MIS is usually a new surgical approach, i.e. two incision surgery or a modified posterior approach which I prefer. If the surgery is carried out with ideal MIS instrumentation, I feel that MIS is less tissue disruptive than mini-incision surgery.

I have read your information on instrumentation and surgical technique for MIHR^®. However, conventional hip arthroplasty with Metal on Metal articulation is gaining popularity as an option for primary hip replacement rather than being used to revise failed resurfacing Arthoplasty. Have you developed bespoke instrumentation for MoM hip Arthoplasty to be delivered through a minimally invasive surgical approach?

Mr Chana: Click here to download Mr Chana's answer