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THR: Trial Reduction and Determination of Leg Length

- Discussion:
    - main goal is to prevent THR dislocation but also to maintain optimal offset;
    - prior to reducing the hip, ensure that center of femoral head is approximately at level of the greater trochanter;
    - once trial reduction has been completed, the trial acetabular liner is removed, the remaining acetabular dome screws are inserted (if they have
              not been already) and the definitive liner is inserted;
    - sciatic nerve should be palpated w/ hip in flexion (and leg extened) to ensure that nerve is not under excessive tension (especially if
              leg has been lengthened);
    - polyethylene insertion
    - leg lengths and stability:  (see post operative evaluation)
              - once the stem and cup have been implanted there are only 3 variables that can optimize length and stability (acetabular
                          liner, head diameter, and neck length); see femoral offset;
              - leg length can be modified by increasing or decreasing neck length;
              - generally the surgeon wants the lowest neck length possible without comprimising stability;
              - intraoperative leg length is determined by preoperative templates, intraoperative x-rays, distances between Steinman pins,
                      and shuck test
              - shuck test:
                      - relative amount of motion achieved when femur is distracted away from the acetabulum - usually about 5 mm);                 
                      - note that spinal anesthesia will allow at least 3 mm of additional shuck as compared to GEA;
                            - references:
                                   - Three Intraoperative Methods to Determine Limb-length Discrepancy in THA
                                   - Effect of anesthesia type on limb length discrepancy after total hip arthroplasty.
                                   - Intraoperative limb length measurement in total hip arthroplasty
              - be sure to take each of these variables into consideration when determining final neck length;
              - note that if a Steinman pin as been used to retract the medius, it should be removed at this point, since it may placed
                        signficant tension on the medius and give a false sense of hip stability;
              - references:
                        - Achieving the required medial offset and limb length in total hip arthroplasty.
                        - Predicting leg-length change after total hip arthroplasty by measuring preoperative hip flexion under general anaesthesia.
                        - The effect of preop lateral flexibility of lumbar spine on perceived leg length discrepancy after total hip arthroplasty.

    - management of increased leg length and increased soft tissue tension:
           - in some cases there will be good stability but increase in leg length with increased soft tissue tension (absence of shuck);
           - if there is excessive soft tissue tension (absence of any shuck with traction), consider recutting the femoral neck at a lower
                 level, inorder to (decrease vertical offset) and then minimally increasing femoral neck length;
                 - becuase femoral components usually have a 35 deg neck angle to horizontal, a longer neck length will increase horizontal
                          offset > verticle ht;
           - when recutting the femoral neck, ensure that final trial broach can be driven further distally w/o causing a femur frx (see
                 broaching technique);
           - goal of this technique is restore optimal shuck without having to further increase modular neck length;
    - difficult reduction:
           - capsule might have to be further released, esp if head and neck segment was short preoperatively;
           - if reduction is not possible & leg is lengthened, then recut neck;
    - management of residual posterior instability:
           - goal is to avoid postoperative dislocation;
           - at 90 deg of flexion & neutral abduction, internal rotation should be w/o impingment or instability to at least 45 deg;
                  - note point of subluxation w/ hip in flexion, adduction & internal rotation;
                  - if hip dislocates easily & head can be manually distracted from socket > few milimeters then some intervention is needed;
           - anterior impingement and capsular tightness:
                  - look for anterior osteophytes which might cause impingement and subsequent posterior subluxation;
                         - these osteophytes are removed up to the capsular layer;
                  - capsule might have to be further released, esp if head and neck segment was short preoperatively;
                         - a tight anterior capsule will cause posterior subluxation even if components are optimally positioned;
                         - the capsule can be released or elevated up to the point of causing anterior subluxation;
           - femoral anteversion:
                  - if modular neck size is significantly longer than was templated, then re-evaluate the patient's total anteversion (ie
                         summation of native femoral and acetabular anteversion) and the total anteversion of the components (anteversion of
                         the cup and femoral stem);
                         - consider changing the version of one or both components, and rechecking stability;
                  - if femoral anteversion is insufficient, then consider a femoral stem with built in anteversion;
                  - references:
                         - Factors predisposing to dislocation after primary total hip arthroplasty.  A multivariate analysis.
                         - The effect of anteversion on femoral component stability assessed by radiostereometric analysis
                         - Femoral anteversion and restricted range of motion in total hip prostheses.
           - insufficient soft tissue tension:
                  - determine whether there is enough horizontal offset (from preoperative templates);
                  - options include choosing a stem with increased femoral horizontal offset and then increasing modular neck length; 
                  - also note that insufficient length increases risk for impingement of the femur against the pelvis at the extremes of motion;
                  - if excessive lengthening of extermity would result from longer neck length, then osteotomize greater troch & transfer it
                          distally to help stabilize the hip;
    - anterior instability:
           - if hip cannot be brought into full extension then use shorter neck;
           - if there was a severe flexion contracture preop, release psoas tendon;
           - in extension & neutral abduction, there should be no impingement of posterior polyethylene rim at 45 deg of external rotation;
                  - consider 20 deg lipped liner is substituted to relieve impingement;
           - posterior trochanter:
                  - if trochanter is located posteriorly, as in DDH, postraumatic disorders, hypertropic arthritis
                  - perform osteotomy of greater trochanter & transfer it laterally;
                  - w/ impingment in external rotation, consider removing bone from the posterior greater trochanter

 Position, orientation and component interaction in dislocation of the total hip prosthesis.

 Factors predisposing to dislocation after primary total hip arthroplasty. A multivariate analysis.

 Stem design and dislocation after revision total hip arthroplasty: clinical results and computer modeling.

 Uncemented total hip arthroplasty with subtrochanteric derotational osteotomy for severe femoral anteversion.

 Management of limb length inequality during total hip replacement.

 Effect of Anesthesia Type on Limb Length Discrepancy After Total Hip Arthroplasty

The influence of femoral offset on health-related quality of life after total hip replacement

True or apparent leg length discrepancy: which is a better predictor of short-term functional outcomes after total hip arthroplasty?