Introduction: Radiolucent lines (RLL) underneath the tibial component are common findings following the Oxford Uni-compartmental Knee Arthroplasty (OUKA)[1]. Many theories have been proposed to explain the cause of RLL, such as poor cementing, osteonecrosis, micromotion, and thermal necrosis, however, the true aetiology and clinical significance remain unclear. We undertook a retrospective study analysing the association between RLL and pre-operative, intra-operative factors, as well as clinical outcome scores.

Method: One hundred and sixty-one knees which had undergone primary Phase 3 medial Oxford OUKA were included in the study. Fluoroscopic radiography films were assessed at five years post-operatively for areas of tibial RLL. The presence of RLL was compared to

patients’ pre-operative demographics for age, weight, height, BMI,

Results: Of the 161 knees in the study, 126 (78%) were found to have tibial RLL. No statistical difference was found between knees with RLL and those without in terms of preoperative demographics, intra-operative factors, or clinical assessment criteria.

Discussion: No clear relationship between RLL, preoperative demographics, and intra-operative factors has been identified in this study. We conclude that tibial RLL following OUKA is a common finding but do not seem to affect medium term clinical outcome.

Purpose: To compare the site of lesions in medial and lateral unicompartmental osteoarthritis (OA) of the knee.

Methods: Patients with medial (n=35) and lateral (n=15) OA, having unicompartmental knee arthroplasty, were recruited. Intra-operatively, the distance between the anterior, posterior, medial and lateral margins of the full-thickness lesion and reference lines dividing the condyles was measured. The midpoints of lesions were calculated and groups were compared. Lateral radiographs were used to determine the relationship between the lesion site and knee flexion angle (KFA).

Results: Femoral lesion: In lateral OA, the midpoint of lesions was 25.0mm (SD:8.8) posterior to the reference line passing transversely through the apex of the inter-condylar notch. This was significantly different (p< 0.001) from midpoint in medial OA, which was 10.7mm (SD:9.4) posterior to the reference line.

Tibial lesion: In lateral OA, the midpoint of lesions was 2.0mm (SD:6.5) posterior to the reference line passing through the mid-coronal plane of the resected tibia. This was located significantly more posterior (p=0.038) than midpoint in medial OA, which was 2.2mm (SD:5.7) anterior to the reference line.

Knee Flexion Angle: In lateral OA, the midpoint of lesions was on average at 40° flexion and sites of smaller lesions were very variable. The lesion expanded both anteriorly and posteriorly. In medial OA, smaller femoral lesions occurred in full extension and extended further posteriorly with disease progression.

No significant difference was demonstrated in medial and lateral localisation of the lesions.

Conclusion: Medial OA begins near full extension, progresses in a predictable manner and is perhaps initiated by events occurring at heel strike. Lateral OA begins in flexion in a less predictable manner, at KFA above that seen during the gait cycle. The different sites of lesions in medial and lateral OA suggest different aetiology and pathophysiology. Therefore, prevention and treatment strategies should be different.

Purpose: Varus deformity after total knee replacement (TKR) is associated with poor outcome. This aim of this study was to determine whether the same is true for medial unicompartmental arthroplasty (UKA).

Methods: 158 patients implanted with the Oxford UKA, using a minimally invasive approach, were studied prospectively for five years. Leg alignment was measured with a long-arm goniometer referenced from Anterior Superior Iliac Spine, centre of patella and centre of ankle. Patients were grouped according to the American Knee Society Score (AKSS). Group A: > 0° varus (n=13, 8.2%); Group B: 0 to 4° valgus (n=39, 24.7%); Group C: 5–10° valgus (normal alignment, n=106, 67.12%). Comparisons were made between the three groups in terms of the absolute and the change in Oxford Knee Score (OKS) and AKSS over the five year period, and the presence of radiolucency.

Results: There was no significant difference in any outcome measure except for Objective-AKSS (p< 0.001). The means and standard deviations of the ΔOKS for the groups were:

24 ± 5,

The frequency of five year radiolucency for the groups A, B, and C were 42%, 35%, and 45% respectively.

Conclusion: The aim of the Oxford UKA is to restore knee kinematics and thus knee alignment to the pre-disease state. Therefore, as demonstrated by this study, about 30% of patients have varus alignment. This study also demonstrates that post-operative varus alignment does not compromise the outcome. The only score which did show worse outcome was the Objective-AKSS. This is because 10 or 20 points are deducted for varus alignment, which is not appropriate following UKA. Therefore, AKSS in its present form is not a reliable tool for assessment of UKA.

Purpose: To evaluate the effects of underhanging/overhanging tibial components on clinical outcome following the Oxford unicompartmental knee arthroplasty (UKA), and to identify an acceptable sizing limit.

Method: One hundred and sixty-three knees which had undergone the Phase 3 medial Oxford UKA (Biomet, Swindon) were measured. Based on five-year post-operative radiographs, they were divided into groups with tibial component underhang (n=38), none or minimal overhang of less than three millimetres (n=121), and a group with overhang equal to or in excess of three millimetres (n=13). Clinical outcome was assessed by changes in the twelve-question Oxford Knee Score (ΔOKS) and pain score (ΔPS) component (questions 1,4,5,8,9) from pre-operative assessment to five years following surgery.

Results: At five years after surgery, ΔOKS was significantly worse in the overhang group compared to both the neutral and underhang groups (p=0.015, and p=0.028 respectively). ΔPS was also shown to be significantly worse between the overhang and the neutral group (p=0.026 respectively).

Conclusion: Appropriate sizing of the tibial component is essential to optimise load bearing in total knee arthroplasty. In UKA such sizing is critical due to halving of the bony support for the tibial component and the lack of room for a large stem. Excessive undersizing of the prosthesis may lead to subsidence and loosening, whilst excessive overhanging may cause local soft tissue irritation and pain.

This study demonstrates that medial overhang of less than three millimetres for the tibial component is acceptable in the Oxford UKA. Excessive overhang equal to this or more results in significantly worse ΔOKS and ΔPS. However, no difference in the five year ΔOKS and ΔPS was demonstrated between underhang and the other two groups in this study.

Purpose: To identify associative factors for radiolucency (RL) under the tibial component following the Oxford unicompartmental arthroplasty (UKA), and to evaluate its effect on clinical outcome scores.

Method: One hundred and sixty-one knees which had undergone primary Phase 3 medial Oxford UKA were included. Fluoroscopic radiography films were assessed at five years post-operatively for areas of tibial RL. The two groups of patients, with and without RL, were compared to

patients’ pre-operative demographics for age, weight, height, BMI,

Results: 101 (62%) knees were found to have tibial RL. All RL were categorised as physiological or they were < 1mm thick, with sclerotic margins and non-progressive. No statistical difference was found between knees with RL and those without, in terms of pre-operative demographics, intra- or post-operative factors, and clinical outcome scores (p> 0.1 in all variables).

Discussion: Radiolucency (RL) under the tibial component is a common finding following the Oxford UKA. Many theories have been proposed to explain the cause of RL, such as poor cementing, osteonecrosis, micromotion, and thermal necrosis. However, the true aetiology and clinical significance remain unclear. We attempted to address this.

We found no significant relationship between physiological RL, pre-operative demographics, intra-operative variables and clinical outcome scores in this study. Tibial RL remains a common finding following the Oxford UKA yet we do not know why it occurs but in the medium term, clinical outcome is not influenced by RL. In particular, it is not a sign of loosening. Physiological RL can therefore be ignored even if associated with adverse symptoms following the Oxford UKA.

Introduction: Arthroscopic ankle arthrodesis is an effective treatment for end-stage arthritis.

A screw that has any thread across the fusion site can not offer any compression and may be postulated to lower the rate of fusion. Similarly, maximal screw thread in the target bone would optimise fixation.

This retrospective study calculates the ideal characteristics of a screw used for ankle arthrodesis, and assesses the correlation between the lack of compression and non-union.

Method: Fifty-one consecutive patients(102 screws) who have had arthroscopic ankle fusions were studied. Either AO(n=38) or ACE(n=64) screws were used. We calculated the screw-thread distance that crossed the talotibial(TT) or the subtalar(ST) joints on digitised images, and recorded the outcomes of the fusions.

Result: Of the 38 AO screws, only one (2.6%) had threads across the TT joint(thread-length into the joint = 1.2mm). None of the ST joints had been breached.

Of the 64 ACE screws, 8(12.5%) had threads across the TT joint, representing 7(21.9%) of all posterior screws and 1(3%) of all anterior screws in the study. The mean length of screw-threads into the TT joint was 2.1mm(range 0.53 to 4.06 mm). The ST joints were breached by 4(6.25%) screws(all posterior). The mean length of protrusion was 1.8mm(range 0.28 to 3.89mm). No screw thread crossed both TT and ST joints simultaneously.

No non-unions were recorded in either group.

Discussion: In our study the use of ACE screws for arthroscopic arthrodesis increases the risk of screw-threads breaching either the TT or ST joints when compared to the use of AO screws.

Conclusion: We conclude a thread length of 19–20mm would optimise fixation/compression. However no clinical correlation was demonstrated between reduced compression and non-union in this study.