Introduction
Materials and methods
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Both cruciate ligaments functionally intact.
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Full-thickness cartilage in the lateral compartment.
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Correctable intra-articular varus deformity (based on clinical assessment).
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Full-thickness cartilage loss in the medial compartment.
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Contra-indication for MRI.
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All forms of inflammatory arthritis.
Operative technique
Outcome measures
Primary outcome measure: radiological assessment of component positioning
Radiographic parameter | Optimum position |
---|---|
Femoral component: varus/valgus angle (AP radiograph) | <10.0° varus to <10.0° valgus |
Femoral component: flexion/extension angle (LA radiograph) | 15.0° flexion to <0° extension |
Tibial component: varus/valgus angle (AP radiograph) | <5.0° varus to <5.0° valgus |
Tibial component: posterior tilt (slope) angle (LA radiograph) | Within ±5.0° of the 0° baseline (“Baseline” taken as 7.0° posterior tilt but this is recorded as 0°) |
Tibial component: medial fit (AP radiograph) | Flush or <2.0 mm overhang |
Tibial component: anterior fit (LA radiograph) | Flush or <2.0 mm overhang |
Tibial component: posterior fit (LA radiograph) | Flush or <5.0 mm underhang |
Secondary outcome measures
Assessment of functional outcome
Intra-operative assessment of surgical accuracy
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Correspondence between the implanted and planned component sizes.
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The need to perform a horizontal tibial “re-cut”.
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Tracking of the meniscal bearing (measured as the distance from bearing to the metal upright of the tibial component in flexion and extension).
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Size of the meniscal bearing inserted (optimum bearing size considered as 3 or 4 mm).
Statistical analysis
Results
Participant demographics
Demographic | Patient-specific instrumentation (n = 23) | Conventional instrumentation (n = 22) |
p value |
---|---|---|---|
Mean age (range) in years | 66.9 (52.2–77.1) | 68.2 (51.0–88.2) | n.s. |
Sex (M:F) | 10:13 | 13:9 | n.s. |
Median ASA (range) | 2 (1–3) | 2 (1–3) | n.s. |
Mean body mass index (range) | 29.8 (23.8–40.3) | 31.8 (22.2–39.5) | n.s. |
Mean operative time (range) in minutes | 75.3 (53.0–90.0) | 63.5 min (50.0–82.0) | 0.001** |
Primary outcome measure: radiological assessment of component positioning
Radiographic parameter | Patient-specific instrumentation | Conventional instrumentation |
p value (means) |
---|---|---|---|
Mean (SD) | Mean (SD) | ||
Femur: varus/valgus angle | 0.9° varus (4.0) | 1.8° varus (3.0) | n.s. |
Femur: flexion/extension angle | 9.1° flexion (3.0) | 8.8° flexion (4.8) | n.s. |
Tibia: varus/valgus angle | 3.5° varus (2.9) | 4.0° varus (2.1) | n.s. |
Tibia: posterior tilt angle | 1.8° superior (2.8) | 3.7° superior (2.1) | 0.029** |
Tibia: medial fit | 0 mm (1.0) | 1.0 mm underhang (1.3) | n.s. |
Tibia: anterior fit | 1.0 mm underhang (0.9) | 1.0 mm underhang (0.7) | n.s. |
Tibia: posterior fit | 0 mm (0.8) | 0 mm (0.9) | n.s. |
Radiographic parameter | Patient-specific instrumentation (n = 23) | Conventional instrumentation (n = 22) |
p value |
---|---|---|---|
Number of outliers [%] | Number of outliers [%] | ||
Femur: varus/valgus angle | 1 (varus) [4%] | None | n.s. |
Femur: flexion/extension angle | None | 1 (flexed) [5%] | n.s. |
Tibia: varus/valgus angle | 5 (all varus) [22%] | 6 (all varus) [27%] | n.s. |
Tibia: posterior tilt angle | 2 (1 superior, 1 inferior) [9%] | 5 (all superior) [3%] | n.s. |
Tibia: medial fit | None | 1 (underhang) [5%] | n.s. |
Tibia: anterior fit | None | None | NA |
Tibia: posterior fit | None | 1 (overhang) [5%] | n.s. |
Secondary outcome measures
Assessment of functional outcome
Mean Oxford Knee Score, OKS (range) | Patient-specific instrumentation (n = 23) | Conventional instrumentation (n = 22) |
p value |
---|---|---|---|
Pre-op OKS | 24.1 (12–38) | 23.3 (10–37) | n.s. |
Post-op OKS | 42.4 (21–48) | 41.5 (26–48) | n.s. |
Δ OKS | 18.3 (4–31) | 18.2 (5–31) | n.s. |
Intra-operative assessment of surgical accuracy
Patient-specific instrumentation (n = 23) | Conventional instrumentation (n = 22) |
p value | |
---|---|---|---|
Cases requiring horizontal “re-cut” of the tibial plateau | 3 | 2 | n.s. |
Median (and interquartile range) distance between the bearing to the metal upright of the tibial component wall | Flexion: 1 mm (1–2) Extension: 2 mm (1–2.5) | Flexion: 1 mm (1–1.5) Extension: 1 mm (1–2) | n.s. n.s. |