Biomechanical Study Comparing Cut-out Resistance of the X-Bolt® and Dynamic Hip Screw at Various Tip-Apex Distances.

BACKGROUND: Bone quality in hip fractures is poor and there is a need to not only correctly position metalwork within the femoral head, but also for implants to resist cut-out. New implant designs may help to reduce metalwork cut-out, leading to fewer failures of fixation. This study compared the cut-out strength of a Dynamic Hip Screw (DHS) to that of an X-Bolt® (X-Bolt Orthopaedics, Dublin, Ireland) implant in an osteoporotic Sawbones® (Sawbones, Vashon Island, WA) model. METHODS: An unstable fracture model (AO 31-A2) was created using low-density 5 pound per cubic foot (pcf) Sawbones®. The DHS and X-Bolts® were inserted into the Sawbones® femoral head at Tip-Apex Distances (TAD) of 10mm, 15mm, 20mm, 25mm, 30mm and 40mm. A cyclic-loading Instron® machine (Instron Corp., Norwood, MA) pushed the bone at a compression rate of 5mm per minute at a 20-degree angle to the axis of the implant with an upper force limit of 4000N. Maximum force reached and load to failure, defined as movement of the implant by 5mm, were recorded. Four implants were used per group to give a total of 48 tests between the two groups. RESULTS: The X-Bolt® demonstrated a superior average maximum total load push-out force compared to the DHS group for all of the TAD configurations tested. The maximum force reached in the X-Bolt® group was significantly higher than that in the DHS group at a TAD of 10mm (X-Bolt® 3299.25N vs. DHS 2843.75N, P<0.029) and 30mm (X-Bolt® 2908.25N vs. DHS 2030N, P<0.029). The X-Bolt® also had a higher load to failure than the DHS group at all of the TAD values tested. CONCLUSIONS: The X-Bolt® implant gave superior performance compared to the standard DHS, as reflected by a greater push-out force in an osteoporotic Sawbones® model.

Registry Data-Valuable Lessons But Beware the Confounders.

A mature national joint registry with widespread adoption and audit can successfully demonstrate trends and influence future orthopedic practice. Correlations can be identified; however, this should not be misinterpreted as causality. It is essential to consider confounding when analyzing observational datasets.

Outcomes of infected revision knee arthroplasty managed by two-stage revision in a tertiary referral centre.

BACKGROUND: A two-stage revision remains the gold standard to eradicate deep infection in total knee arthroplasty. Higher failure rates are associated with a number of factors including poly-microbial infections, multiresistant organisms and previous operations. The aims are to investigate [1] the overall success rate of a two-stage revision for infections in TKA, [2] the outcome of repeat two-stage revisions in recurrent infections and [3] the factors affecting the outcomes of such cases. METHODS: We present the outcomes of a consecutive, retrospective case series of 51 periprosthetic joint infections managed with a two-stage revision knee arthroplasty over a three year period. RESULTS: Forty-six (90%) of 51 were referred from other hospitals. Infection was successfully eradicated in 24 (65%) of 37 patients undergoing an initial two-stage procedure. Following a failed two-stage revision, a repeat two-stage revision was performed in 19 patients eradicating infection in 8 (42%). A third two-stage was performed in five of these patients eradicating infection in three with an average follow-up of 43 months. Multidrug resistance was present in 69%, and 47% of the patients were infected with multiple organisms. All unsuccessful outcomes involved at least one multidrug-resistant organism compared to 43% in the successful cohort (P=0.0002). Serological markers prior to a second-stage procedure were not significantly different between successful and unsuccessful outcome groups. CONCLUSION: Single or multiple two-stage revisions can eradicate infection despite previous failed attempts. In this series, failure is associated with multidrug resistance, previous failed attempts to eradicate infection and a less favourable host response.

In vivo roughening of retrieved total knee arthroplasty femoral components.

BACKGROUND: Joint registry data highlights the higher rates of cumulative revision for younger patients undergoing TKR. One of the reasons associated with this higher revision rate may be due to the wear of the UHMWPE leading to loosening. Alternate bearing surfaces have been developed to address this problem; however, roughening of the metal bearing surface has not been demonstrated in vivo. METHOD: We recorded roughness measurements of retrieved femoral components. RESULTS: Average lateral condyle roughness was 0.032 µm, compared to control values of 0.020 µm, p=0.002; average medial condyle roughness was 0.028 µm, compared to a control value of 0.019, p<0.001. CONCLUSION: There was a small but statistically significant roughening of femoral components in vivo compared to controls. This may have important implications for aseptic loosening of knee arthroplasty components and the decision to use scratch resistant components.

Gluteal necrosis following pelvic fracture and bilateral internal iliac embolization: Reconstruction using a transposition flap based on the lumbar artery perforators.

INTRODUCTION: The use of bilateral internal iliac artery embolization to control hemorrhage associated with pelvic fractures is a life saving intervention. Gluteal necrosis is a rare but potentially fatal complication of this procedure. Following debridement, reconstruction can present a considerable challenge due to the compromised vascularity of local tissue. PRESENTATION OF CASE: A 17 year old girl suffered an open book pelvic fracture following a road traffic accident. In order to stop profuse bleeding, bilateral internal iliac artery embolization was performed. This procedure was complicated by the development of right sided gluteal necrosis. Following extensive debridement, a transposition flap based on the lumbar artery perforators was performed to cover the soft tissue defect. DISCUSSION: Gluteal necrosis occurs in approximately 3% of cases following internal iliac artery embolization. Following complete excision of the devitalised tissue reconstructive surgery is necessary. Local flaps are suboptimal options when the integument supplied by branches of the internal iliac arteries has been compromised following embolization. Furthermore, the use of a free flap is restricted by the lack of a readily accessible undamaged recipient vessel. In the present case a transposition flap based on the lumbar artery perforators facilitated robust reconstruction of the buttock region. CONCLUSION: To avoid sepsis, it is imperative that gluteal necrosis following internal iliac artery embolization is recognized and promptly debrided. A transposition flap based on the lumbar artery perforators is a good option for subsequent soft tissue coverage, which avoids use of tissue supplied by the branches of the internal iliac arteries.