Purpose of the study: The communicating branch of the lateral plantar nerve is an anastomotic branch between the medial and lateral plantar nerves. Morton’s pseudoneuroma is usually described as resulting from the combination of one of the divisions of the medial plantar nerve and the communicating branch of the lateral plantar nerve. Surgical treatment of Morton’s pseudoneuroma can fail, leading to recurrent neuroma, or digital hypoesthesia. We performed an anatomic dissection study to search for the anatomic basis for an improved surgical technique.

Material and methods: The study included 35 feet of embalmed cadavers. A standard protocol was used for dissection. We studied the communicating branch, its frequency and size, and measured its attachment on the 3rd and 4th plantar common digital nerves. All other nerve ramifications were noted.

Results: None of the 35 dissected feet presented a macroscopic Morton pseudoneuroma. The communicating branch was present in 77% of the specimens with frequent anatomic variations concerning the size, ramifications, orientation and distance from the intermetatarsal ligament. A fine plantar cutaneous branch was often found under the intermetatarsal ligament. The bifurcation of the 2^nd and 3^rd nerves was occasions not far from the junction of the communicating branch on the 3^rd nerve, raising the risk of injury to the 2^nd nerve during surgical excision of a Morton pseudoneuroma.

Discussion: The communicating branch appears to play a role in recurrence after excision of the Morton pseudoneuroma by preventing the retraction of the 3^rd digital nerve in the muscle zone if it is not sectioned. However, wide resection of the proximal part of the 3^rd nerve and the communicating branch could lead to digital hypoesthesis if the 2^nd digital nerve is injured. The proximity of the bifurcations of the 2^nd and 3^rd nerves and of the 3^rd nerve with the communicating branch could explain this type of complication.

Conclusion: We advocate resection of the pseudoneuroma under visual control in order to carefully resect the communicating branch without injuring the adjacent nerve branches.

Purpose: The quality of implantation of single-compartment knee prostheses is a recognised prognostic factor. Acceptable reproducibility can be achieved with traditional instrumentations, although the rate of error can be significant. Computer-assisted implantation might improve results. Most of the currently proposed techniques require supplementary preoperative imaging or implantation of metallic material for guidance. The Orthopilot® system is a purely peroperative system and could thus provide better cost-effectiveness.

Material and methods: We implanted 30 single-compartment knee prostheses using the Orthopilot® computerised system (Aesculap, Chaumont, Group A) and compared the radiographic quality of the implant on telemetric AP and lateral views with those from a control group of 30 single-compartment prostheses implanted with a traditional instrumentation with a femoral centromedullary aiming device (group B). All patients underwent surgery for primary degeneration and were operated on by the same surgeon using the same implant (Search®, Aesculap, Chaumont). The control group was selected among a consecutive series of 250 implants to match the study group for age, gender, importance of the degeneration and frontal femorotibial mechanical angle.

Results: The mechanical femorotibial angle was within desired limits (177±3°) in 26 patients in group A and in 20 patients in group B. Frontal orientation of the femoral component was within desired limits (90±2°) in 27 patients in group A and in 19 in group B (p< 0.05). Frontal orientation of the tibial piece was within desired limits (90±2°) in 27 patients in group A and in 19 patients in group B (p < 0.02). The original level of the joint line was reconstructed with a 2 mm margin in 30 patients in group A and in 24 patients in group B (p < 0.05). Eighteen patients in group A and four patients in group B had optimal implantation for all criteria studied (p < 0.001). There were no system-related complications.

Discussion, conclusion: Computer-assisted implantation is more reliable and more reproducible than traditional instrumentation for the implantation of a single-compartment knee prosthesis. Follow-up results with these prostheses may be better. Systematic preoperative imaging, or preoperative implantation of metallic guide pins is not necessary with this system. The system appears to offer a better cost-effectiveness.

Purpose: The biepicondylar axis of the femur is considered by many authors as a reliable reference axis for flexion-extension of the knee and to establish desirable orientation of the femoral component of a total knee arthroplasty. We studied the reproducibility of axis measurments made using an automatic digital acquisition system (OrthoPilot®, Aesculap, Chaumont, France). The system localises anatomic points in space from information obtained with a palpation probe carrying an infrared diode.

Material and methods: A consecutive series of 20 total knee arthroplasties (Search®, Aesculap, Chaumont, France) implanted by two senior surgeons on the same surgical team were studied. The mechanical axis of the femur was calculated prior to the study using kinematic acquisition of the position of the centres of rotation of the hip and the knee. The frontal reference plane was then defined from the most posterior point on the femoral condyles palpated with the probe as the plane containing the mechanical axis of the femur and parallel to the posterior bicondylar line. The apex of the two femoral epicondyles was obtained by direct palpation with the probe. A second plane passing through the apex of the epicondyles and parallel to the mechanical axis of the femur was thus defined. Three acquisitions were made for the same patient by each of the two surgeons without changing the posterior bicondylar reference plane. The angle between the frontal plane of reference and the biepicondylar plane was calculated directly by the software for each acquisition. The variability of the three measurements taken by each operator and between the two operators was studied with the Wilcoxon test for paired series and with Spearman’s coefficient of correlation.

Results: Mean intraobserver variability for the orientation of the biepicondylar axis was 4° for the two operators, with a maximum of 11° for the first operator and 9° for the second, the directions being random. The mean interobserver variability for this orientation was 4° with a maximum of 14°, again at random. All differences were statistically significant.

Discussion, conclusion: Measurements of the biepicondylar axis exhibit high intra- and interobserver variability, probably due to the anatomic conditions; the apex of the epicondyles is a blunt surface difficult to identify with precision. Use of this axis to determine the rotation of the femoral component of a total knee arthroplasty is thus an element of wide variability with measurement inaccuracy of a mean ± 5° but with a maximum that can reach 10°. The question remains to determine whether this uncertainty is tolerable or whether more precision is required.