Corrosion at the neck-stem junction as a cause of metal ion release and pseudotumour formation

We present a series of 35 patients (19 men and 16 women) with a mean age of 64 years (36.7 to 75.9), who underwent total hip replacement using the ESKA dual-modular short stem with metal on-polyethylene bearing surfaces. This implant has a modular neck section in addition to the modular head. Of these patients, three presented with increasing post-operative pain due to pseudotumour formation that resulted from corrosion at the modular neck-stem junction. These patients underwent further surgery and aseptic lymphocytic vaculitis associated lesions were demonstrated on histological analysis. Retrieval analysis of two modular necks showed corrosion at the neck-stem taper. Blood cobalt and chromium levels were measured at a mean of nine months (3 to 28) following surgery. These were compared with the levels in seven control patients (three men and four women) with a mean age of 53.4 years (32.1 to 64.1), who had an identical prosthesis and articulation but with a prosthesis that had no modularity at neck-stem junction. The mean blood levels of cobalt in the study group were raised at 50.75 nmol/l (5 to 145) compared with 5.6 nmol/l (2 to 13) in control patients. Corrosion at neck-stem tapers has been identified as an important source of metal ion release and pseudotumour formation requiring revision surgery. Finite element modelling of the dual modular stem demonstrated high stresses at the modular stem-neck junction. Dual modular cobalt-chrome hip prostheses should be used with caution due to these concerns.

Computer navigated total knee arthroplasty: aspects of a single unit's experience of 777 cases

The use of computer navigation and conventional techniques in total knee arthroplasty remains controversial. Advocates of computer navigated techniques cite better alignment of components and reduced morbidity associated with avoidance of intramedullary instrumentation as a rationale for their use. In contrast, proponents of conventional techniques argue that better alignment does not correlate with a better functional outcome and that the conventional approach avoids the perceived risk of fracture associated with bicortical insertion of navigation tracker pins. All total knee arthoplasties performed at our institution are prospectively monitored for life in a dedicated Joint Replacement Assessment Clinic (JRAC). Patients are reviewed by physiotherapists, independent of the surgeons who performed surgery, both preoperatively and at six weeks, three and six months, and one, two and five years postoperatively (and every five years thereafter). Patients are assessed using validated outcome measures (Knee Society Score, Western Ontario and McMaster Universities (WOMAC) osteoarthritis index, Short Form SF-36 Health Survey (version 2) and a patient satisfaction score). In addition, at 6 months post surgery, a CT scan of each implanted prosthesis is performed using the Perth CT knee protocol. The findings of a single unit's experience of 777 navigated primary total knee replacements are discussed and critically compared to the body of literature that currently relates to this controversial topic.

Computer navigation versus conventional total knee replacement

We previously compared the component alignment in total knee replacement using a computer-navigated technique with a conventional jig-based method. We randomly allocated 71 patients to undergo either computer-navigated or conventional replacement. An improved alignment was seen in the computer-navigated group.

The patients were then followed up post-operatively for two years, using the Knee Society score, the Short Form-36 health survey, the Western Ontario and McMaster Universities osteoarthritis index, the Bartlett Patellar pain questionnaire and the Oxford knee score, to assess functional outcome.

At two years post-operatively 60 patients were available for assessment, 30 in each group and 62 patients completed a postal survey. No patient in either group had undergone revision. All variables were analysed for differences between the groups either by Student’s t-test or the Mann-Whitney U test. Differences between the two groups did not reach significance for any of the outcome measures at any time point. At two years postoperatively, the frequency of mild to severe anterior pain was not significantly different (p = 0.818), varying between 44% (14) for the computer-navigated group, and 47% (14) for the conventionally-replaced group. The Bartlett Patellar score and the Oxford knee score were also not significantly different (t-test p = 0.161 and p = 0.607, respectively).

The clinical outcome of the patients with a computer-navigated knee replacement appears to be no different to that of a more conventional jig-based technique at two years post-operatively, despite the better alignment achieved with computer-navigated surgery.

Computer navigation of the acetabular component

Our aim was to assess the intra- and inter-observer reliability in the establishment of the anterior pelvic plane used in imageless computer-assisted navigation. From this we determined the subsequent effects on version and inclination of the acetabular component.

A cadaver model was developed with a specifically-designed rod which held the component tracker at a fixed orientation to the pelvis, leaving the anterior pelvic plane as the only variable. Eight surgeons determined the anterior pelvic plane by palpating and registering the bony landmarks as reference points. The exact anterior pelvic plane was then established by using anatomically-placed bone screws as reference points.

The difference between the surgeons was found to be highly significant (p < 0.001). The variation was significantly larger for anteversion (sd 9.6°) than for inclination (sd 6.3°). The present method for registering pelvic landmarks shows significant inaccuracy, which highlights the need for improved methods of registration before this technique is considered to be safe.

Computer-assisted knee arthroplasty versus a conventional jig-based technique

We have compared a new technique of computer-assisted knee arthroplasty with the current conventional jig-based technique in 70 patients randomly allocated to receive either of the methods. Post-operative CT was performed according to the Perth CT Knee Arthroplasty protocol and pre- and post-operative Maquet views of the limb were taken. Intra-operative and peri-operative morbidity data were collected and blood loss measured.

Post-operative CT showed a significant improvement in the alignment of the components using computer-assisted surgery in regard to femoral varus/valgus (p = 0.032), femoral rotation (p = 0.001), tibial varus/valgus (p = 0.047) tibial posterior slope (p = 0.0001), tibial rotation (p = 0.011) and femorotibial mismatch (p = 0.037). Standing alignment was also improved (p = 0.004) and blood loss was less (p = 0.0001). Computer-assisted surgery took longer with a mean increase of 13 minutes (p = 0.0001).

Fractured Whiteside Ortholoc II knee components

A comprehensive failure analysis was performed on 6 femoral components and 1 tibial component that fractured in service. All were Whiteside Ortholoc II total knee arthroplasty components, manufactured from cast cobalt-chromium-molybdenum alloy and porous coated. Fracture surface analysis revealed fatigue-induced failure in all cases. Most fractures occurred at regions of high stress concentration, such as sharp corners, sintered beads, and thin sections. Metallurgical examination showed significant variation in grain size, interdendritic carbides, and hardness between samples. In some cases, continuous carbide networks and voids were prominent at the bead-substrate interface. Patient weight and surgical placement were identified as contributory factors in component failure. Limitations of cast cobalt-chromium-molybdenum alloy in weight-bearing applications must be emphasized, particularly when important determinants, such as design, metallurgy, and specific clinical factors, are less than optimal.

Massive pulmonary thromboembolism after manipulation of an unstable pelvic fracture: a case report and review of the literature

Acute pulmonary thromboembolism has not been reported in association with manipulation of an unstable pelvic fracture. We report a case of pulmonary thromboembolism following manipulation of an unstable pelvic fracture one week after injury.

The long-term success of fresh, small fragment osteochondral allografts used for intraarticular post-traumatic defects in the knee joint

Ninety-two fresh osteochondral allografts were implanted in 91 patients with posttraumatic osteoarticular defects of the knee joint. These patients have been prospectively followed since 1972. An analysis of long-term survival of these grafts has been performed to determine their success rates: 75% at 5 years, 64% at 10 years, and 63% at 14 years. An evaluation was made between unipolar grafts, which involve only one surface of the compartment, and bipolar grafts, which involve both surfaces. The unipolar grafts had a lower failure rate at all time periods compared to bipolar grafts, with 76% survival at 5 years, 69% at 10 years, and 67% at 14 years. While investigating other factors that might affect the survival of the fresh osteochondral allografts, we calculated the influence of the anatomical location of the graft, patient sex, and patient age. There was no meaningful impact on allograft survival by either the location of the allograft or the sex of the patient. However, there was a significant effect on allograft longevity in terms of patient age, with patients under age 60 doing better. The best indication for the use of unipolar fresh osteochondral allografts is for posttraumatic defects in relatively young, active patients. Joint malalignment should be corrected to achieve best results.

Fresh osteochondral allografts for post-traumatic defects in the knee. A survivorship analysis

Fresh osteochondral allografts were used to repair post-traumatic osteoarticular defects in 92 knees. At the time of grafting, varus or valgus deformities were corrected by upper tibial or supracondylar femoral osteotomies. A survivorship analysis was performed in which failure was defined as the need for a revision operation or the persistence of the pre-operative symptoms. There was a 75% success rate at five years, 64% at ten years and 63% at 14 years. The failure rate was higher for bipolar grafts than for unipolar and the results in patients over the age of 60 years were poor. The outcome did not depend on the sex of the patient and the results of allografts in the medial and lateral compartments of the knee were similar. Careful patient selection, correction of joint malalignment by osteotomy, and rigid fixation of the graft are all mandatory requirements for success. We recommend this method for the treatment of post-traumatic osteochondral defects in the knees of relatively young and active patients.

Disassembly of a one-piece metal-backed acetabular component. A case report

We report a case of late dissociation of a one-piece metal-backed acetabular component, associated with a prolific soft-tissue reaction to the polyethylene debris. The polyethylene liner was not visible on the radiographs. The metal-backed shell could not be removed because of bone ingrowth. We recommend that modular systems be utilised in cementless arthroplasty of the hip and that radiographic markers be incorporated in the polyethylene of the acetabular cup.

Increasing initial interactions among integrated EMR students and their nonretarded peers in a game-playing situation

Two ways of increasing the initial interaction among integrated EMR students and their nonretarded classmates in a game-playing situation were examined. Three hundred and four randomly assigned intermediate school students observed classmates about to play a simple game and were asked to select partners and opponents from two pairs of students matched on sex and grade. The experimental pair had 1 EMR student and 1 nonretarded student; the control pair had 2 nonretarded students. The subjects' past knowledge of the pair members served as a covariate in the design to determine whether past knowledge influenced their selections of pair members. Each subject was also provided information regarding the competency level of each pair member in relation to the particular game. Results indicated that the covariate was not a significant factor in the selection process; however, the appended competency statement and the game-playing option were found to be highly significant in influencing selection of the pair members and increasing the selection of the EMR child by his nonretarded classmate.