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- Clinical (pain-free, mobile knee) and mechanical goals
- Four main objectives:
- Restore mechanical alignment
- Establish joint line perpendicular to mechanical axis
- Achieve soft tissue balance
- Restore normal Q angle and joint alignment
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- Medial parapatellar
- Subvastus
- Preserves quadriceps strength and vascularity
- Midvastus
- Preserves lateral half of VMO insertion
- Lateral parapatellar
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- Quad snip
- VY turn down
- Tibial tuberosity osteotomy (TTO)
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- Kinematic vs Mechanical Alignment
- Mechanical Axis Method = cut femur and tibia both perpendicular to MA (more commonly used)
- Kinematic Axis Method = cutting femur in 9 deg valgus (3 deg more) and tibia in 3 deg varus to re-establish the normal joint line orientation which is 3 degree varus
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- Done with IM jig, set to 6 degrees valgus (difference between AA and MA) → becomes perpendicular to MAF
- Cut less if there is valgus knee (hypoplastic femoral condyle)
- The taller the person, the smaller the angle
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- For this cut, use the 4-in-one cutting guide
- To place the 4-in-one guide in the correct position, we need to:
- Get the rotation correct
- Get the size correct
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- Perpendicular to Whiteside's line
- Parallel to transepicondylar line
- 3° external rotation (because tibia plateau is in 3 degrees of varus)
- Do not use posterior condyles in lateral condyle hypoplasia in valgus knee
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- Femur Chamfer cuts +/- box cut
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- Done with EM jig, align to tibial crest and center of ankle
- Controls for varus/valgus and tibial slope
- Tibial slope 3-5 degrees
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- Prior to this, adjust rotation by placing trial implant, flex and extend knee until auto-adjusted
- Make a mark at tibial tuberosity (typically medial 1/3), then align keel punch to it
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- A line drawn from the deepest part of the trochlea groove to the centre of the intercondylar notch posteriorly
- It is perpendicular to the transepicondylar line
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- Intraop alignment - with 3 reference lines (Whiteside's AP line, transepicondylar axis, posterior condylar axis) before anterior and posterior cuts
- Implant positioning - avoid medialization and internal rotation of tibial and femoral implants [Avoid functional increase in Q angle]
- Avoid lateralization of patellar component
- Intraop assessment - release tourniquet and assess maltracking (Study found that tourniquet deflation leads to better tracking and saved 30% of releases - JOA Husted et al.
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- Anterior referencing uses a boom = cut posterior = prevents notching but risks increasing flexion gap
- Posterior referencing = cut anterior = risk of notching but flexion gap is controlled
- I usually use anterior referencing
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- Measured resection = bone cuts made using bony landmarks
- Gap balancing = equalizing soft tissue tension before performing bone cuts
- I use the measured resection technique, where bone cuts are made independent of soft tissue tension based on the 3 reference lines. A spacer block is then used to examine the flexion and extension gaps.
- In contrast, with gap balancing, soft tissue tension is assumed to be correct (it's not altered) and is used to determine bone cuts
- Studies show no difference between techniques
MR vs GB.pdf2340.9KB
GB vs MR no diff.pdf1348.8KB
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- The goal is to create rectangular and equal flexion and extension gaps
- McPherson's Rule
- Flexion gap is controlled by posterior femur cut, tibial cut, and PCL (if the flexion gap is tight, you can release the PCL just enough to reduce tightness)
- Extension gap is controlled by distal femur cut, tibial cut, and posterior capsule
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- Excessive distal femoral resection
- Requires distal femoral augmentation
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- Undersized implant, incompetent PCL, or excessive tibial slope
- Solutions include augmenting the posterior femoral condyle or shifting the femoral component posteriorly while avoiding notching
- Alternatively, you can increase the extension gap by cutting more distal femur, then use a thicker polyethylene insert
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- There's no consensus on this practice. In theory, electrocautery denervates the patella, reducing pain
- However, Gupta et al. (2010 JBJS) demonstrated no difference in pain outcomes between denervated and non-denervated patients
Gupta 2010.pdf199.1 KB
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- Stay medial to PCL with single prong retractor (do not go lateral to PCL)
- Popliteal artery is a lateral structure at level of joint line
- Flexion brings popliteal artery further away
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- Resect distal femur for more extension gap (every 10° of FFD, cut more by 2mm)
- Sequence of release for posterior impingement:
- Osteophytes → posterior capsule → gastrocnemius muscle origin
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- [PS knees] Femoral Cam Jump due to loose flexion gap
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- Fibrous nodule at junction of posterior superior aspect of patella and quads tendon → repeated entrapment → inflammation and synovial proliferation → pain
- Management:
- Non-operative
- Arthroscopic debridement
- [PS knees] Tibial post fracture due to hyperextension from loose extension gap or excessive posterior slope
- Aseptic loosening
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- Types:
- Extension instability
- Mid-flexion instability
- Loose flexion gap/ruptured PCL
- Flexion instability
- Excess flexion gap
- Recurvatum (common in NM disorders e.g., Polio)
- Management = Consider revision – may need constrained knee
- Dissatisfaction rate - 10-20%
- DVT
- Notching - reduces the load needed to cause a fracture
- Common peroneal nerve palsy - especially in valgus knees
- Vascular injury
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- Patellar clunk
- Diagnosis - painful, palpable catch as knee extends at 40° flexion
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- Pre-op factors - Patella baja
- Implant factors - PS > CR
- Surgeon factors:
- Femur/tibia - increased posterior femoral condylar offset, femoral component in flexed position
- Patellar - Low patellar component exposing unresurfaced superior pole
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Bilateral/Obese TKR?
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- Controversial. Consider if significant FFD and varus will affect rehabilitation
- Meta-analysis by HSS 2013 shows increased mortality rates at 30 days, 3 months, and 1 year
- 2021 Journal of Arthroplasty Metaanalysis by Makaram et al.:
- Decreased infection rates and length of stay
- But increased 90-day mortality and DVT
- Similar revision rates
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- WHO definition: BMI > 30
- Considerations:
- Preoperative weight loss program
- Plan for additional manpower
- IV antibiotics dosed according to weight
- Longer incision for adequate exposure
- Navigation – potentially reduces operation time and improves alignment
- DVT prophylaxis – obesity is a risk factor
- Prophylactic stem use?
- Steere et al. 2018: BMI > 35, no difference in failure rates between stem vs. no stem
- Outcomes:
- Increased risk of infection, loosening, and revision
Sterre 2018.pdf449.1 KB
TKR for varus knee
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- Osteophytes ➔ Deep MCL ➔ assess whether flexion or extension is tight
- If tight in flexion ➔ release anterior sMCL
- If tight in extension ➔ release Posterior oblique portion of sMCL, PM capsule, semi-membranosus, and Pes Anserinus
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- Tibial reduction osteotomy – use smaller tray and lateralize tray
- Medial epicondyle osteotomy – fixation is optional ➔ typically results in fibrous non-union
Blood Loss Management
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- 500ml to 1L
- Expect hemoglobin drop of 1 to 3 g/dl
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- Preop – optimize hemoglobin, screen for anemia, optimize chronic diseases (CKD, sickle cell)
- Intraop –
- IV TXA as per NICE guidelines
- Tourniquet
- Cell saver
- Good hemostasis
- Post-op – avoid drain
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- I will not insert a drain
- Cochrane review by Martyn Parker 2007 – No difference in infection, hematoma, wound dehiscence, or reoperations, BUT more blood transfusions with drain use.
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- Results consistently show TXA reduces transfusion requirements
- NICE Guidelines recommend 1g IV TXA and 1g intra-articular after final washout. https://www.nice.org.uk/guidance/ng157/chapter/Recommendations#tranexamic-acid-to-minimise-blood-loss
- Method of administration (IV vs. topical) and dosing (high vs. low) show no significant differences
- Topical TXA is diluted in normal saline and injected into the joint with or without a drain
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- Yes, tourniquets can reduce postoperative blood loss
- However, they do not decrease transfusion rates
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A man is commended according to his good sense, but one of twisted mind is despised. Proverbs 12:8