Aims

Hip resurfacing remains a potentially valuable surgical procedure for appropriately-selected patients with optimised implant choices. However, concern regarding high early failure rates continues to undermine confidence in use. A large contributor to failure is adverse local tissue reactions around metal-on-metal (MoM) bearing surfaces. Such phenomena have been well-explored around MoM total hip arthroplasties, but comparable data in equivalent hip resurfacing procedures is lacking. In order to define genetic predisposition, we performed a case-control study investigating the role of human leucocyte antigen (HLA) genotype in the development of pseudotumours around MoM hip resurfacings.

Hip resurfacing may be a useful surgical procedure when patient selection is correct and only implants with superior performance are used. In order to establish a body of evidence in relation to hip resurfacing, pseudotumour formation and its genetic predisposition, we performed a case-control study investigating the role of HLA genotype in the development of pseudotumour around MoM hip resurfacings.

All metal-on-metal (MoM) hip resurfacings performed in the history of the institution were assessed. A total of 392 hip resurfacings were performed by 12 surgeons between February 1st 2005 and October 31st 2007. In all cases, pseudotumour was confirmed in the preoperative setting on Metal Artefact Reduction Sequencing (MARS) MRI. Controls were matched by implant (ASR or BHR) and absence of pseudotumour was confirmed on MRI. Blood samples from all cases and controls underwent genetic analysis using Next Generation Sequencing (NGS) assessing for the following alleles of 11 HLA loci (A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPB1, DPA1). Statistical significance was determined using a Fisher's exact test or Chi-Squared test given the small sample size to quantify the clinical association between HLA genotype and the need for revision surgery due to pseudotumour.

Both groups were matched for implant type (55% ASR, 45% BHR in both the case and control groups). According to the ALVAL histological classification described by Kurmis et al., the majority of cases (63%, n=10) were found to have group 2 histological findings. Four cases (25%) had group 3 histological findings and 2 (12%) patients had group 4 findings. Of the 11 HLA loci analysed, 2 were significantly associated with a higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) and 4 were noted to be protective against pseudotumour formation (DQA1*03:01:01, DRB1*04:04:01, C*01:02:01, B*27:05:02).

These findings further develop the knowledge base around specific HLA genotypes and their role in the development of pseudotumour formation in MoM hip resurfacing. Specifically, the two alleles at higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) in MoM hip resurfacing should be noted, particularly as patient-specific genotype-dependent surgical treatments continue to develop in the future.

Little is known about how arthroscopic knots behave in terms of reverse slippage and creep during the first few hours following a Bankart repair. We aimed to assess differences between knot types tied with a variety of suture materials when exposed to loading which might be expected during the first 12 hours following a repair.

This study uses an apparatus to model the tensioning of a slipknot, the closing of a Bankart lesion and any reverse slippage occurring on removal of the tensioning force. Eight examples each of the Duncan loop and SMC knots were tied by an experienced surgeon using 4 different suture materials (PDS, Ethibond, Panacryl, Fibrewire). An arthroscopic knotting technique was used utilising a knot pusher. Each knot was locked with 3 half-hitches alternating direction and post each time. Any reverse slippage occurring during the tying process was recorded. Each knot was then left in situ for 12 hours under loads equivalent to a repaired Bankart lesion and any subsequent reverse slippage was recorded at the end of this period.

After initial passing of the Duncan loop the sutures were ranked inversely to size of suture loop (resistance to slippage) in order Panacryl (5.08±0.15mm); Fibrewire (5.7±1.03mm); Ethibond (7.22±3.47mm) and PDS (8.2±5.16mm). After passing of locking hitches, they ranked Ethibond (5.13±0.24mm); PDS (5.15±0.09mm); Panacryl (5.17±0.13mm) and Fibrewire (5.66±0.5mm – significant p< 0.05). After 12 hrs, some evidence of reverse slippage was noted, Ethibond (5.23±0.27mm); PDS (5.27±0.13mm); Panacryl (5.3±0.16mm) and Fibrewire (5.66±0.5mm – significant p< 0.05). The SMC knot showed similar results.

If a slip-knot back slips it can be tightened with the first locking hitch. After this further hitches do not tighten the knot further. Some slippage was noted during the first 12 hrs. Using arthroscopic techniques, Fibrewire performs less well than other materials.