The impact of free-radical stabilization techniques on in vivo subsurface mechanical properties in highly cross-linked polyethylene acetabular liners.

Highly cross-linked polyethylene (HXLPE) for total hip arthroplasty was developed to improve wear resistance in vivo and associated complications in comparison to ultrahigh molecular weight polyethylene. This material typically goes through various free-radical stabilization techniques by remelting, single-annealing, or sequentially annealing the polyethylene to improve in vivo oxidation and wear properties. The purpose of this study is to determine if there is evidence of subsurface microhardness changes in retrieved HXLPE liner at the rim and articular subsurface after extended in vivo time that could be associated with oxidation and its effects on mechanical properties and implant integrity. Retrieved HXLPE liners were chosen based on peak subsurface Fourier transform infrared spectroscopy oxidation values. Each was mechanically tested for subsurface microhardness at both the rim and articular surface using a validated microindentation technique. Rim testing demonstrated a decrease in mechanical integrity that corresponded to higher subsurface oxidation values regardless of the free-radical stabilization technique. At the articular surface, a decrease in mechanical integrity was observed near the surface corresponding to peak oxidation and Vicker's hardness, which decreased with increasing depths. This was found in all groups, with the exception of the single-annealed liners, which demonstrated decreased mechanical integrity trends at greater depths between 1.0 and 2.0 mm. Our results suggest that subsurface mechanical properties do change in vivo for certain implants. Though it is likely that the mechanical failures are multifactorial, we have shown that mechanical property degradation of HXLPE liners does occur with long-term in vivo exposure and should be considered a possible risk factor.

A Rare Case of Metallosis Co-occurring With Chronic Prosthetic Joint Infection in Total Hip Arthroplasty.

Prosthetic joint infection (PJI) and metallosis are known complications of total hip arthroplasty (THA) and are causes for revision surgeries. Articulating metal surfaces in total hip arthroplasty with corrosion at modular junctions can lead to the release of metal ions that can cause an immune-mediated biological reaction. There are few cases in the literature of both coinciding together. We describe a case of chronic Cutibacertium acnes PJI and metallosis co-occurring in a 64-year-old female after THA with a dual mobility construct. After undergoing uncomplicated left THA through a modified Hardinge approach, the patient dislocated anteriorly after four weeks and required revision of her acetabular component to a less anteverted position. Nine months later, she presented with hip pain and was found to have medial wall fragmentation and cystic changes around the greater trochanter on radiographs, elevated serum cobalt and chromium levels, and a benign noninfected hip aspiration. During her revision procedure, intraoperative histopathology showed over 20 neutrophils per high power field in multiple samples and fluid aspirates demonstrating Gram-positive rods. She was also found to have pseudotumor formation with the erosion of the anterior and posterior capsules with black debris on the femoral stem trunnion and the backside of the modular dual mobility liner. An antibiotic spacer was placed and her cultures grew into C. acnes. She completed six weeks of intravenous ceftriaxone and, during her "drug holiday," she dislocated her spacer and was found to have a lateral femoral diaphyseal stress fracture at the distal end of her spacer. She underwent stage II of her revision, and while the plan was to continue her antibiotics, she had an adverse reaction and was transitioned to oral antibiotics for six months. Due to delayed healing, she underwent additional irrigation and debridement with head and liner exchange. Her wound then healed, and at her one-year final follow-up, she was able to ambulate without pain, and her serum inflammatory and metal ion levels were within normal limits. Concurrent PJI and metallosis from articulating metal interfaces can occur, and a high index of suspicion is necessary to properly manage both conditions.

Direct anterior approach for femoral component revision: Surgical technique for extended trochanteric osteotomy and anterior cortical window.

OBJECTIVE: Direct anterior approach (DAA) is becoming a popular option for both primary and revision total hip arthroplasty (THA). Adequate exposure is crucial in the setting of revision THA. The purpose of this article is to describe two different techniques for expanded femoral exposure through the DAA, the anterior extended trochanteric osteotomy and anterior cortical window. METHODS: Extensile exposure were carried out in cadavers, using the contralateral hip as a control. The exposure and technical viability were assessed. RESULTS: It was demonstrated that both extensile techniques can be carried out safely. CONCLUSIONS: Extensile exposures including femoral osteotomies can be safely carried out for revision THA via DAA.

Distal tibia allograft for glenohumeral instability: does radius of curvature match?

BACKGROUND: A distal tibia osteochondral allograft is a potential graft option for glenoid reconstruction because the distal tibia may have a similar radius of curvature (ROC) as the glenoid. This study evaluated ROC mismatch as measured on computed tomography (CT) scans between the glenoid, distal tibia, and humeral head. METHODS: Bilateral CT images were formatted for 10 decedents from the Office of the Medical Investigator database, giving 20 specimens per anatomic location. The ROCs of the glenoid, distal tibia, and humeral head were measured. A statistical model was generated to assess ROC mismatch of randomly paired distal tibias and glenoids. RESULTS: The mean ± standard deviation ROC was 2.9 ± 0.25 cm for the glenoid, 2.3 ± 0.21 cm for the distal tibia, and 2.5 ± 0.12 cm for the humeral head. No differences were found in laterality, intraobserver, or interobserver measurements. The least-squares difference in the ROC between the glenoid and tibia was 0.57 cm, glenoid and humerus was 0.40 cm, and humerus and tibia was 0.17 cm. Only 22% of randomly paired distal tibias and glenoids had a difference in ROC of 0.3 cm or less. CONCLUSION: CT measurement of the ROC of the glenoid, distal tibia, and humeral head is reliable and reproducible. The probability of obtaining a random distal tibia allograft with a similar ROC to the glenoid is low. Obtaining ROC measurements of the injured glenoid and the distal tibia allograft specimen before use for glenoid reconstruction may be useful.