Purpose: This study examines the structural performance of different devices for the fixation of supracondylar femoral ‘T’-type intra-articular fractures.

Methods: A finite element model was developed to examine three commonly used devices for fixation of ‘T’-type unstable fractures of the distal femur:-

a retrograde distal femoral nail with condylar bolts and multi-planar locking screws,

The distal femoral geometry was been taken from the BEL repository. The bone was aligned with the mechanical axis and a compressive load of 2000N and separately a torsion load of 10Nm were applied. A fracture was introduced by removing a transverse 15mm slice of material and a saggital slice of 1mm thickness.

The FE model examined whether any of the constructs was markedly stiffer than any other.

Results: Both intra-medullary nail constructs were stiffer than the DCS, with the nail with condylar bolts and multi-planar screws being stiffer than the nail with only two parallel distal locking screws. The nail with condylar bolts did, however, produce significant levels of stress within the bone before any axial load was applied – particularly in the region adjacent to the end washers. Under torsion, the nail constructs were always more effective than the side plate construct.

Conclusions: This FE model demonstrates that fixation of supracondylar femoral ‘T’-type fractures is mechanically superior with retrograde nails rather than DCS constructs. Fixation with a retrograde nail with condylar bolts plus multiplanar screws gives the stiffest fixation. High stresses are seen around the condylar bolts, but if the bone quality is adequate then the additional stiffness achieved is significant. These results support the clinical use of intra-medullary nails with compression bolts and multi-planar screws for the fixation of this type of fracture.

Aim: To accurately identify the meniscofemoral ligaments in cadaveric human specimens, and to determine anatomical variations in the posterior cruciate ligament that may lead to mis-identification of these structures.

Methods: A total of 79 fresh frozen knees were examined from 45 cadavers Combined anterior and posterior approaches were used to inspect the vicinity of the posterior cruciate ligament (PCL) for the presence of the anterior and posterior meniscofemoral ligaments. The anterior approach utilised a medial parapatellar incision followed by division of the anterior cruciate ligament, whilst a midline posterior arthrotomy was used for the posterior approach. Further dissection facilitated inspection of the meniscal and femoral attachments of the MFLs, and measurement of their lengths. Videos of MFL and PCL motion during passive flexion of the cadaveric were also performed.

Results: In total, 74 (94%) of the 79 specimens contained at least one meniscofemoral ligament. The posterior meniscofemoral ligament (pMFL) was present in 56 (71%) specimens, whilst the anterior meniscofemoral ligament (aMFL) was present in 58 specimens (73%). Both ligaments coexisted in 40 (51%) of knees. In 15 specimens the PCL was seen to have oblique fibres, which attached proximal to the tibial attachment of the main part of the PCL. We termed this “the false pMFL”, as it could be easily mis-identified as the posterior meniscofemoral ligament. Several other anatomical variations were also identified. The mean length of the aMFL was 20.7±3.9mm, whilst that of the pMFL was 23±4.2mm. Although the lengths of the MFLs were relatively constant, there was a wide variation in thickness.

Discussion: This study confirms the high incidence of at least one MFL in humans, which suggests a functional role for these structures. The oblique fibres of the PCL can be readily mis-identfied as the pMFL. These caveats should be borne in mind, during both arthroscopic examination and in the interpretation of magnetic resonance imaging (MRI) scans of the knee. Although some variations of the MFLs have been reported on MRI imaging2, there has been no note of the oblique fibres of the PCL reported in the present study. As this variation was present in almost one in five of our specimens, its appearance on MRI scanning requires investigation.

The function of the meniscofemoral ligaments is undetermined, although many hypotheses comment on a role in guiding the motion of the lateral meniscus during knee flexion. Other possibilities include a function as a secondary restraint supplementing the posterior cruciate ligament.

Aims: To determine load to failure for four different meniscal repair techniques, and to assess gapping across repairs under cyclical loading.

Background: Studies comparing the biomechanical properties of different meniscal repair systems are limited, and most have simply investigated load to failure. Meniscal tissue is highly anisotropic, and far weaker under tension in the radial direction. Load to failure using high loads may, therefore, not be the most physiologically relevant in-vitro test for repair of circumferential tears, and measuring increases in gapping across repair sites under cyclical loading at lower loads may be of greater importance.

Methods: Bovine menisci were divided vertically, 5mm from the peripheral edge to simulate a circumferential tear, and then repaired using one to four techniques: vertical loop sutures using 1 -PDS, bioabsorbable Meniscal Arrows (Atlantech), Meniscal Fasteners (Mitek) or T-Fix Suture Bars (Acufex). Nine specimens were tested in each group using an Instron 5500 materials testing machine to determine load to failure. A further nine specimens in each group were tested by cyclic loading between 5N and 10N at 20mm/min for 25 cycles, using a digital micrometer to measure initial gapping, and a Differential Variable Reluctance Transducer to measure the progressive increase in gapping across the repair site during the cyclical loading. Data was analysed by ANOVA and Tukey’s multiple comparison post test using Prism (GraphPad) software.

Results: The mean loads to failure (with s.d.) in Newtons were: Sutures 72.7 (22.0), Arrows 34.2 (15.4), Fasteners 40.8 (13.4), and T-Fix 49.1 (13.8). The load to failure was significantly greater with the Sutures compared to the Arrows (p< 0.001), the Fasteners (p< 0.001) or the T-Fix (p< 0.05).

The mean gapping across the repairs after 25 load cycles (with s.d.) in millimetres was: Sutures 3.3 (1.0), Arrows 2.2 (0.9), Fasteners 4.0 (0.6) and TFix 3.5 (0.7). The mean gapping was significantly less for the Arrows compared to the Sutures (p< 0.05), the Fasteners (p< 0.01), or the T-Fix (p< 0.05).

Conclusions: These results confirm that meniscal repair by suturing gives the highest load to failure, but show that Arrows give superior hold with the least increase in gapping across a repair under cyclical loading by this test protocol.