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- Patient factors (3)
- Age > 55
- BMI < 30
- No inflammatory arthritis - RA, gout
- Disease Factors (4)
- Minimal mal-alignment: Varus < 10°, Valgus < 5°
- Intact cruciate and collateral ligaments
- < 10° FFD
- Pain only at medial compartment; no PFJOA
- However, indications have broadened, for example:
- ACL - differentiate between acute ACL rupture (where concomitant ACL reconstruction is possible) versus chronic ACL deficiency with no instability
- PFJOA - acceptable when OA changes on medial side rather than lateral side
Erasmus.PRINCIPLES OF UNICONDYLAR KNEE ARTHROPLASTY.pdf67.0KB
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- UKA aims not to over-correct deformity, but also avoid under-correction which leads to varus malposition and higher risk of failure
- Residual varus > 5-7° is associated with increased risk of revision
- NEVER release the MCL
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- Fixed = flat design allowing more natural knee kinematics, but has higher contact pressure resulting in more wear
- Mobile = Curved poly with higher conformity and reduced contact pressure
- Mobile bearings are technically more difficult to implant
- Overall – similar revision rates but different failure mechanisms
- Fixed bearings fail due to PE wear
- Mobile bearings fail due to dislocation
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- Cementless UKA may have increased risk of periprosthetic fracture
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- Controversial. No, it can be classified into 2 types of ACL deficiency:
- Primary ACL deficiency from trauma → has instability
- Secondary ACL deficiency from degeneration → usually no instability
- Primary ACL tear from trauma with instability should not undergo UKA
- ACL deficiency secondary to OA can be considered, with studies showing good short to mid-term outcomes
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- This remains controversial with no clear consensus
- Hamilton et al. in JBJS reported a 15-year follow-up of 805 knees with mobile bearing UKA
- The suitability depends on which area of the patella has osteoarthritis
- Severe damage to the LATERAL side of PFJ remains a contraindication
- OA changes on the MEDIAL side, regardless of severity, do not compromise function or survival
- Preoperative anterior knee pain does not compromise functional outcome or survival
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- On the medial side, it occurs in 1 in 200 cases - usually anteriorly
- On the lateral side - 10% incidence!
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- Technical factors - component malposition, unbalanced flexion/extension gap, impingement
- Patient factors - trauma injuring the MCL
- Complication-related - infection, aseptic loosening
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- The lateral collateral ligament is slack in flexion, unlike the medial side where the MCL remains tight
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- Bearing exchange to a larger spacer
- Revision UKA, consider fixed bearing design
- Conversion to TKR, with constrained knee implant on standby
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- Systematic review by Dettoni et al. found no difference in mid and long term follow up of up to 10 years. Survival for both is 80% for both at 10 years
- They differ slightly in
- Indications - HTO is suited for patients who are of high demand, UKA usually more in low demand patients. Previous HTO
- Technical goals - HTO aim to over correct while UKA does not aim to correct alignment
- Conversion challenges to TKR -
- 77% of UKA group needed osseous reconstruction due to bone loss
- More UKA revision needed revision implants like augments and stems
- HTO higher complication rates e.g. infection due to more soft tissue dissection
UKA to TKR Conversion
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- Revision stages: preoperative, intraoperative, postoperative
- Preoperative - Prepare standby equipment and explant sets
- Intraoperative - EEERR
- E - Extend previous incision
- E - Explant UKA
- E - Examine bone loss (using AORI classification)
- R - Reconstruct bone defects
- R - Replace with zonal fixation principles (consider stems)
- Postoperative - Full weight-bearing as tolerated (FWBAT)
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- Patient Factors - Osteoporosis, Female gender
- Anatomical factors
- Proximal tibia vara - Medial Eminence line is extra-medullary, reducing bone volume supporting the tibial component.
- Surgeon Technical factors -
- Damage to posterior cortex
- Vertical overcutting of medial plateau
- Improper pin site for tibial cutting block fixation
- Cementless UKA - no consensus as studies show comparable fracture incidences.
- However, excessive interference fit in cementless UKA combined with impaction technique may increase risk
- https://pubmed.ncbi.nlm.nih.gov/33528591/
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- Management depends on fracture displacement and stability:
- If unstable → revision to UKA or TKR
- If stable:
- Undisplaced → conservative management with non-weight bearing (NWB)
- Displaced → Buttress plating
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From the fruit of his mouth a man is satisfied with good, and the work of a man's hand comes back to him. Proverbs 12:13