Planning a Total Knee Replacement & Tibial Osteotomy to Replace & Realign the Knee Joint

The patient (male, age 53) has a history of hypophosphatemic rickets. The associated bone abnormalities and leg mal-alignment had been addressed by bilateral closing wedge tibial osteotomies when the patient was approximately 40 years of age. The patient was now experiencing pain in both knees and was having difficulty walking. 

Considering the right leg first, examination of the long leg weight bearing AP x-ray shows good mechanical axis alignment but a significantly oblique knee joint line (Figure 1). It was apparent that mild osteoarthritis had become worse over time, presumably as a result of the joint obliquity. 

With the AP long leg x-ray loaded into the OrthoView application, the Mechanical Axis Deviation (MAD) Wizard from the Limb Deformity Correction (LDC) Module was used.  

This confirmed that the knee joint line convergence angle was outside normal range. Specifically, using the nomenclature developed by Paley et al., the mLDFA (mechanical Lateral Distal Femoral Angle) and MPTA (Medial Proximal Tibial Angle) were 7.5 degrees and 10 degrees outside normal range respectively.  

All values out of range are highlighted in red in Figure 2.  

Surgical strategies were now considered. Whilst combined femoral and tibial osteotomies could have corrected the joint obliquity, it was judged that the joint surfaces were too badly damaged.  

A total knee replacement (TKR) would replace the worn joint surfaces; however, it would not be possible to achieve correct alignment with a TKR alone since this would involve cutting ligaments. A combined proximal tibial osteotomy and TKR were therefore proposed and the subject of a detailed pre-operative plan. 

The first goal of the planning phase was to demonstrate the feasibility of the proposed, and relatively complex, surgery. Important questions included: 

• What would be the effect of the tibial osteotomy on overall leg alignment and length? 
• What would be the impact of the proposed TKR cuts and tibial osteotomy on the soft tissues? 
• Would the surgery result in good stability and be likely to heal well? 

Using the axis definers in OrthoView’s LDC Module, a CORA was established which identified the magnitude of the angulation correction required as 18 degrees. A cut was added, a dome cut being preferred to an opening wedge as the latter would be too large and unstable in this case. An inverted dome cut was preferred over the standard orientation (as shown) to make it easier to avoid the patellar tendon. 

On-screen ‘reduction’ identifies the following: 

1. No post-operative change in leg length 
2. An indication of the saw blade radius 
3. Location of where the mechanical axis passes through the knee joint. Note: Although medialized, this was judged to be acceptable. 

Having completed planning for the tibial osteotomy, the next phase of the plan was to use OrthoView’s ‘Add New Procedure’ feature to plan for the TKR. 

A revision system, the Smith & Nephew Legion, was chosen since the optional offset stem would be used to help with fixation of the tibial osteotomy. Since the OrthoView digital orthopaedic template for the Smith & Nephew Legion behaves as a complete interconnected system, mimicking the behavior of the actual implant, templating for the necessary stem offset is possible. 

The resulting pre-operative plan provided not only the sizing of the components, but also positioning of the intra-articular cuts and an insight into how these would subsequently affect ligament balancing. 

• Surgery: The trials for the knee replacement were fitted first, and the knee joint determined to be a good functional fit — ligament balance with the cuts required being a major consideration.  
   
  The osteotomy followed with disruption of the fibula to perform the inverted dome osteotomy and the use of the revision stem to anchor the bone, along with a small plate for added support. Bony union was anticipated to be adequate due to the nature of the dome osteotomy. 
   
• Outcomes: At his 6-week return assessment, the patient was pleased with the progress and results and is now preparing for the left lower limb to also be repaired to improve function via a similar method. 
   
  The union is progressing well with subsequent follow up, and the patient remains very happy with the outcome. 

•  Comment: Clearly preoperative planning is essential with a case like this. In times gone by, planning this surgery would have required the surgeon to trace the x-ray images and apply multiple bits of paper to go through the above steps.  
   
  This study describes a ‘final draft’ of the plan but the software allows many ‘what if’ scenarios, with the ability to very easily return to the beginning of a step. In a case like this, it is gratifying when the templating steps match the intra-operative steps very closely, and having used OrthoView software for multiple complex cases, I can safely say this is a consistent outcome. I would also say that the more complex the case, the more useful the planning software is.