There has recently been a proliferation of image-based knee arthroplasty systems which utilize pre-operative radiological analysis of a patient's anatomy to identify the bone cuts required to correct their mechanical alignment. The aim of this was to assess the accuracy of one such system (Visionaire™, Smith and Nephew Inc.©)

Eleven cadavers were imaged using the Smith and Nephew Visionaire® MRI protocol to enable the production of cutting blocks individualized to the various specimens. These cutting blocks were then used to perform knee replacements on all cadavers. Post-operatively the validated Perth CT protocol was used to assess the position and rotational profile of each implant. These measurements were then compared to the pre-operative plan in order to assess the accuracy of implant placement.

Relative to the pre-operative target parameters, the femoral components were aligned in a mean 0.048° valgus (95% CI – 0.36° to 1.32°) with 1.8° extension (95% CI −0.1° to 4.5°) and externally rotated by a mean 0.66° (95% CI 1.08° internal rotation to 2.4° external rotation.) The tibial components were in a mean 0.29° of varus (95% CI – 0.68° to 1.27°) with a posterior tibial slope of 90.5° (95% CI 89.6° to 92.6°) and internally rotated by a mean 1.7° (range 10.1° internal rotation to 1.1° external rotation.)

The findings of our study suggest that the Visionaire system can produce accurate coronal implant alignment. The saggital and rotational alignment was not as reliable although these parameters may have been more prone to adverse influence by the limitations of the cadaveric model. Patient-matched knee arthroplasty technology offers significant potential benefits to both patient and surgeon and warrants further clinical investigation.

Septic arthritis of the knee is an uncommon complication of arthroscopic anterior cruciate ligament reconstruction, with a reported incidence ranging from 0.14% to 1.7% in recent publications. In this study, we assess the clinical presentation, management and early outcome of patients with septic arthritis of the knee following anterior cruciate ligament reconstruction. Literature on this uncommon complication is sparse.

The North Shore and Auckland City Hospital Orthopaedic databases were searched and 13 patients were identified as having been treated for septic arthritis of the knee following anterior cruciate ligament reconstruction in the period from July 2002 to August 2006. Their clinical records were reviewed to compile information regarding their presentation and management. Five of these patients were also recalled for clinical follow-up at an average time of 16 months. We reviewed knee range of motion, stability, functional testing in vertical and horizontal jumps and radiographic changes. Clinical outcomes were further assessed using the Tenger, Lysholm and International Knee Documentation Committee Scores.

The patients reviewed had a mean age of 26 years and presented to hospital at an average of 16 days after their autologous ACL reconstruction surgery. All had initial elevation of inflammatory markers with a mean CRP of 189mg/L (68 – 295) and mean ESR of 71mm in one hr (10 – 112.) Mean peripheral WCC on presentation was 12.3 (9.5 – 22.4.) Initial knee aspirates were performed on all patients and yielded a mean specimen WCC of 60,900 x 106/L. Of the 13 patients, six had S. epidermidis, three had S. aureus, two Propioniobacterium acnes and one Serratia marcescens. No organism was cultured from one patient’s aspirate. The study patients underwent an average of two surgical interventions, the first being arthroscopic washout in each case. Six patients subsequently underwent open knee joint washouts, four of these having their cruciate grafts removed.

Of the five patients recalled for clinical review, three rated their IKDC knee performance as being significantly worse than their uninjured side. Mean IKDC scores were 63.5 for the affected knee and 97.3 for the contralateral knee. Mean Lysholm knee score was 71.8 at follow-up. Tenger scores prior to ACL reconstruction averaged 4.4, compared to 5.6 on review. Radiographs demonstrated evidence of arthritis that was not apparent pre-operatively in four of the five review patients. These individuals lacked an average 2.8 degrees of extension and 13.4 degrees flexion in comparison to their contralateral knee. Two patients demonstrated clinical instability on examination. The mean single-legged hopping distance was 62.9% horizontally and 96.4% vertically, when comparing the affected knee to the contralateral side.

Staphylococcus epidermidis was the most common pathogen identified in this study. Most patients presenting with this complication will require two or more operative procedures and a prolonged course of intravenous antibiotics. The symptomatic and functional outcomes of septic arthritis associated with recent ACL reconstruction are highly variable, but were found to be worse in those patients requiring graft removal to eradicate their infections. Despite their young age, most of those patients undergoing clinical review had radiographic evidence of early osteoarthritis.

The human hip capsule is a heterogeneous structure contributing greatly to the stability of this joint. A posterior approach to the hip necessarily sacrifices the ischio-femoral ligament but the decision to release the ilio-femoral and pubo-femoral ligaments remains at the discretion of the surgeon. This mechanical study aims to demonstrate that these anterior capsular structures, when left intact, may limit the external rotational range of motion when the variables of femoral offset, leg length and neck version are adjusted at the time of surgery.

A dry bone pelvis-femur model was prepared and registered with the Stryker iNstride Hip Navigation software. A cemented 28 HDPE contemporary cup was inserted at 45° inclination with 20° of anteversion and a revision modular stem implanted in the femoral medullary canal. Artificial ilio-femoral and pubo-femoral ligaments were then prepared from plastinated rubber fabric and mounted in their anatomical positions. Using this model, a range of restoration body sizes was sequentially introduced to vary the offset. The rotational range of motion was then assessed. Repeat measurements were made using + 10mm length bodies across the same offset range. Finally, assessments of rotational range of motion were made using the 19mm body alone while varying neck lengths and degrees of version were trialled. All measurements of external rotation were taken in a position of 0° hip flexion and 0° abduction, as determined using the Stryker iNstride Hip Navigation System.

As femoral offset was increased using our model, there was a progressive loss of external rotation. This consistent restriction of external rotation was further accentuated when +10mm length bodies were trialled across the same range of offsets. When a standard 19mm restoration body was placed and a range of heads trialled, it was again found that increasing neck length consistently correlated with a reduction in external rotation. Varying the restoration neck version with a standard head, it was found that increasing retroversion correlated with an increase in the external rotational range of motion.

The findings of this mechanical study suggest a progressive limitation of hip external rotation with increasing femoral offset and leg length when the anterior capsular structures are intact. Such findings are of importance in pre-operative planning as they suggest that increases in these variables may significantly limit a patient’s range of external rotation unless the anterior hip capsule is released. Such considerations must of course be balanced against the potential to destabilise the hip if too extensive a soft tissue release is performed. The artificial model used in this study is intended to approximate the human hip and its ligaments. The absolute values for rotational range of motion measured using the Stryker hip navigation system are less significant than the overall trend which they suggest. A patient-based study is now planned to further test these findings.