High incidence of femoroacetabular impingement deformity in bi-column acetabular fractures.

INTRODUCTION: Dynamic interaction of cam and pincer deformities can result in pathological contact forces in femoroacetabular impingement (FAI) syndrome. Similar deformities were noted during acetabular fracture reconstruction. We hypothesise that the prevalence of FAI deformity is higher in patients sustaining acetabular fractures than in a control group. METHODS: This retrospective radiographic study compared the parameters that define FAI deformity in 100 patients consecutively admitted to a trauma unit with an acetabular fracture and a control group of 100 patients with lateral compression pelvic fracture without acetabular injury. Both underwent identical clinical imaging. Centre-edge angles (CEA) and alpha angles were used to define patients with pincer, cam, or mixed FAI deformity. RESULTS: There were significantly more patients with FAI deformity in the acetabular fracture group than in the control group (71% vs. 18%, p < 0.0001). There were considerably more fractures involving both anterior and posterior acetabular columns in patients with 'pincer' sockets (p = 0.02, OR = 2.95, 95% CI, 1.12-7.78). CONCLUSIONS: There is a high prevalence of cam and pincer deformities in patients with acetabular fractures, particularly bi-column fractures.

Surgical management of renal cancer metastasis in the humerus: novel use of a trabecular metal spacer.

Humeral metastases from renal cell carcinoma are not uncommon. Current surgical practice centres around adequate tumour resection, but often at the expense of functional outcome. The use of trabecular metal (TM) implants is well described in spine and joint surgery. However, their use as a reconstruction device in osseous tumour surgery has yet to be reported. We present our experience in using a TM vertebral body replacement device (VBR) in treating a patient with painful bilateral diaphyseal humeral metastases. Resection of the tumour resulted in defects which the TM-VBR was able to fill. The defect was then bridged with a locking plate and cables. At 2-year clinical and radiographic review, bony integration and a return to pain free, near-normal function was achieved.

The posterior acetabular wall (PAW): an aid to acetabular orientation at primary THA.

INTRODUCTION: Incorrect acetabular component positioning during total hip arthroplasty (THA) may lead to dislocation, impingement, wear and revision. Surgeons commonly use the transverse acetabular ligament (TAL) as a landmark for acetabular component orientation. The posterior acetabular wall (PAW) is a structure easily viewed on plain radiography and its position can help guide acetabular component position. In this study, we examine the efficacy of preoperative radiographs in predicting cup position relative to the PAW. METHODS: Prospective data was recorded on radiographic findings of the posterior wall (prominent, normal, deficient) on a consecutive series of 200 primary THAs utilising a standardised posterior approach. The final cup position relative to the wall was recorded (prominent, flush, deep). Cup inclination and version were then assessed by postoperative radiography and any instances of dislocation recorded. RESULTS: There were 117 females and 83 males with a mean age of 66.5 years. 154 were recorded as having a normal PAW on radiographs, 152 had the cup positioned in line with the TAL and flush to the PAW. 29 had a deficient PAW and 27 of these had a cup positioned prominently with 17 having a prominent PAW and of these 16 a deep cup position. Postoperative radiographs showed a mean cup version of 20.8° and inclination of 44.7° using this method. There were 21 outliers (10.5%) with no dislocations at a minimum 12-month follow-up. CONCLUSIONS: The TAL is a continuation of the posterior labrum. As such, the posterior wall is a useful adjunct to and surrogate landmark for the TAL. It has the added advantage that it is visible on radiographs and so aids surgical planning with respect to cup positioning.

In vitro influence of stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty.

BACKGROUND AND PURPOSE: Under physiological loads, debonded cemented femoral stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered stems in vitro has shown differences in performance, with greater interface pressures generated by the rough stems. In this study we investigated the individual effects of stem surface finish, degree of mantle wear, and mode of loading on the stem pump mechanism. METHOD: Rough and polished stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational stem movement, and the interface pressures were compared. RESULTS: The pressures generated by the rough and polished stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated. INTERPRETATION: Femoral stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of stem surface finish. The rough surface finish is only important in creating this instability in tapered stems.

In vitro comparison of the effects of rough and polished stem surface finish on pressure generation in cemented hip arthroplasty.

BACKGROUND AND PURPOSE: High pressures around implants can cause bone lysis and loosening. We investigated how pressures are generated around cemented femoral stems. METHOD: We compared the pressures generated by rough and polished tapered stems at their cement interfaces, in an in vitro model, before and after 1 million load cycles. RESULTS: At the start of the study, the loading of both polished and rough stems generated interface pressures that were not statistically significantly different. After 1 million load cycles, the rough stems generated greater interface pressures than at the start (p = 0.03), with maximum pressure wave amplitudes of 450,000 Pa or 3,375 mm Hg. The pressures generated by polished stems were similar before and after 1 million load cycles, and were lower than the pressures generated by the rough stems (p = 0.01). Stem loading caused micromotion between the stem and cement. Polished stems migrated distally in the cement but retained rotational and axial stability. The rough stems also migrated distally and wore the cement mantle, leading to increased rotational instability. INTERPRETATION: The change in the rotational micromotion of the rough stem is likely to be the principal cause of the increased stem pump output and to be a key factor in the longevity of cemented femoral implants.

The use of traction to simplify intramedullary fixation of paediatric forearm fractures.

A minority of paediatric and early adolescent diaphyseal forearm fractures require operative fixation. The method of closed reduction and intramedullary stabilisation of such fractures using stainless steel pins or flexible titanium nails has well documented success rates. The literature proposing their use advises the wires are inserted with the forearm resting free on a radiolucent arm table. In our experience, this technique is demanding; the fracture sites are unstable, often with soft tissue interposition, and the proximal radial fragment is difficult to control by closed means because of the overlying muscle mass. The technique, we describe, employs a standard Maquet Orthostar traction table (Maquet, Colima Ave, Hylton Riverside, Sunderland, UK) to effect a stable closed reduction of diaphyseal forearm fractures to simplify the procedure of passing the radial wire. The traction is then released to allow elbow flexion and the ulna wire to be passed, the ulna fracture having been reduced by the traction and stabilised by the radial wire. In summary, the use of traction to reduce and stabilise the radial fracture has simplified the surgery and reduced operative time.