Saturday, September 20, 2014

Is digital templating of the humeral component worthwhile?

Reliability and accuracy of digital templating for the humeral component of total shoulder arthroplasty

These authors evaluated the interobserver reliability and accuracy of pre-operative digital templating for humeral head size, stem size and neck angle for total shoulder arthroplasty in 25 patients. Four surgeons used pre-operative radiographs and templating software to generate templates of the humeral head, stem and neck for each patient.

Interobserver reliability was fair to substantial (κ = 0.26 to 0.71) for head size, fair to substantial (κ = 0.39 to 0.72) for stem size and slight to fair (κ = 0.16 to 0.34) for neck angle. Templated head size, stem size and neck angle had accuracies of 53%, 77% and 68% within one size variation, respectively.

The authors concluded that digital templating was not a useful guide for pre-operative surgical planning and should not be used to select a prosthesis.

Comment: In our practice, component sizing is determined by intra-operative trialing rather than templating. A potential trap of committing to the humeral stem size seen on the AP view is that the diameter is usually smaller on the lateral view - the humeral canal is not a circle in cross section.  Templating is used to anticipate problems that may be encountered at surgery. For example, the humeri of smaller more elderly individuals may have large endosteal canal diameters, yet a prosthesis that fills this canal may be too large for the proximal humeral metaphysis. 

As another example, posttraumatic malunions leaving the proximal humerus in varus may place the tuberosities over the proximal extrapolation of the canal, warning us that conventional placement of the humeral canal may not be possible.