Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting.

We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation.

Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6 mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1 mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3 mm).

These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology.

Isolated talonavicular arthrodesis is a common procedure particularly for posttraumatic arthritis and rheumatoid arthritis. Two surgical approaches are commonly used: the medial and the dorsal approach. It is recognized that access to the lateral aspect of the talonavicular joint can be limited when using the medial approach and it is our experience that using the dorsal approach addresses this issue.

We performed an anatomical study using cadaver specimens, to compare the amount of articular surface that can be accessed, and therefore prepared for arthodesis, by each surgical approach. Medial and dorsal approaches to the talonavicular joint were performed on each of 11 cadaveric specimens (10 fresh frozen, 1 embalmed). Distraction of the joint was performed as used intraoperatively for preparation of articular surfaces during talonavicular arthrodesis. The accessible area of articular surface was marked for each of the two approaches using a previous reported technique3. Disarticulation was performed and the marked surface area was quantified using an immersion digital microscribe, allowing a three dimensional virtual model of the articular surfaces to be assessed.

The median percentage of accessible total talonavicular articular surface for the medial and dorsal approaches was 71% and 92% respectively. This difference was significant (Wilcoxon Signed Ranks Test, p<0.001).

This study provides quantifiable measurements of the articular surface accessible by the medial and dorsal approaches to the talonavicular joint. These data support for the use of the dorsal approach for talonavicular arthrodesis.

The superficial anterior vasculature of the knee is variably described; most of our information comes from anatomical literature. Descriptions commonly emphasise medial-dominant genicular branches of the popliteal artery. Describing the relative contribution of medial and lateral vessels to the anastomotic network of the anterior knee may help provide grounds for selecting one of a number of popular incisions for arthrotomy.

The aim of this study is to describe the relative contribution of vessels to anastomoses supplying the anterior knee.

Cadaveric knees (n = 16) were used in two cohorts. The first cohort (n = 8) were injected at the popliteal artery with a single colour of latex, and then processed through a modified diaphanisation technique (chemical tissue clearance) before final dissection and analysis. This was repeated for the second cohort, but with initial dissection to identify potential source vessels at their origin. Each source vessel was injected with a different colour of latex. The dominant sources were determined in each specimen.

The majority of the specimens (n = 13; 81%) demonstrated that an intramuscular branch though the vastus medialis muscle was the dominant vessel. Anastomoses were most common over the medial side of the knee, both superiorly and inferiorly (3-5 anastomoses in all cases). Anastomosis over the lateral knee was infrequent (1 anastomosis in 1 specimen).

The results suggest that anterior vasculature of the knee is predominately medial in origin, but not from the genicular branches as previously described. This network of vessels found in the anterior knee is thought to be the main supply to the patella, extensor apparatus, anterior joint capsule and skin.

Optimum placement of incision for arthrotomy is a subject of debate. Considering the main blood supply to the anterior knee may help in choosing a particular approach.