Imaging Findings Page 2

Post-Operative Imaging Findings

Normal Imaging


Conventional radiographs, AP, left, and lateral, right: Note that the humeral prosthesis is in the anatomic position. The scapular implant sits flush with the posterior chest wall. Scapular and humeral components should show no signs of dislocation and there should be no periprosthetic fracture.

Complications

Dislocation

This was the most common complication seen in our series at USC. Testing was performed by Stryker Orthopaedics to demonstrate the amount of weight/torque necessary to dislocate a constrained joint with locking mechanism. The weight required for push-out dislocation (axially extract an assembled liner from the shell) was 514 lbs, while the amount of torque required for cam-out dislocation (dislodge an implant head from the insert after impingement) was 450 in-lbs.25

Conventional radiographs, lateral: At left, the modular humeral prosthesis has dislocated between the intercalary segment (2) and the intramedullary segment (3). This likely occurred because the upper extremity is non-weightbearing and thus subject to gravity's downward pull. At right is the screw-reinforced modular  implant.

Conventional radiographs, AP: Note the dislocated proximal humeral head from an older model scapular prosthesis, below left. Below right is the revised implant, now with new scapular component.


Intra-operative photograph: A pseudomembrane was discovered between the glenoid liner and  the steel glenoid of the scapular prosthesis in the above patient

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Tumor Recurrence

Rates of local recurrence after limb-sparing surgery range between 10-20%.24

60-year old male had axillary tumor recurrence one year after placement of his endoprosthesis

AP conventional radiographs, baseline, above left, and follow-up, above right: Note the left-sided axillary soft tissue density and lack of muscle markings in the follow-up film compared to the baseline film. Also notice the superolateral displacement of the endoprosthesis.

MRI coronal, T1, top, and STIR, bottom: This is the above patient's MR. Note the superolateral displacement of the endoprosthesis (arrow) by the large tumor (outlined in pink), elevating the patient's affected shoulder. This is contrary to the somewhat drooping shoulder that would be expected after such surgery.

T1 MRI, axial: Note axillary tumor recurrence (outlined in blue) in close proximity to left scapular endoprosthesis (arrow).

STIR MRI, axial: Tumor recurrence (outlined in blue) near endoprosthesis (arrow) highlighted by this MR sequence.

Recurrence in Patient With Melanoma

CT, axial: This follow-up CT scan demonstrated no intrathoracic disease. Small axillary lymph nodes are present (arrow).

CT, axial: This scan taken three months later demonstrated enlargement of the axillary lymph nodes (arrows), Biopsy revealed recurrent melanoma.

T1 MRI, axial: Note the enlarged and axillary lymph node (arrow) readily visible on MR imaging.

MRI axial, T1, below left and STIR, below right: Note how the MR tech has positioned the flow artifact so that it does not obscure the area of interest.

MRI, axial: Incidental lung metastasis (arrow) noted on pre-op MR, below.

Additional complications were encountered in our series. No advanced imaging was performed as these were treated based on clinical signs and symptoms. These complications included: 

  •  Tenting of the clavicular remnant with skin ulceration

  •  Periprosthetic hematoma/seroma
  •  Wound necrosis

  • Parasthesias

Though proximal humeral endoprostheses are reported in recent studies to show the highest rates of prosthetic survival and lowest rates of revision, certain complications may be radiologically evident. Complications (and rates) cited in the literature in the past 10 years include:19, 21, 22, 24, 27

  • Periprosthetic fracture (0-0.7%)

  • Deep Infection (0-3.4%)
  • Loosening of the humeral prosthesis (0-10.3%)
  • Stress-shielding (minor bone resorption at the prosthesis-bone junction) (up to 27%)

An interesting caveat is that although evidence of infection is important to look for on follow-up imaging, infection following Tikhoff-Linberg procedure with implant placement will likely involve soft-tissue as there is little or no bone left to infect. Thus, it would be unlikely to observe the classic interface widening between the prosthesis and bone seen in, for example, an infected knee implant. However, this radiographic sign can be observed if the infection involves the humeral stem. It would be in essence indistinguishable from signs of loosening. Advanced imaging, nuclear medicine studies, or image-guided aspiration of fluid pockets can be employed to aid in the differential diagnosis. Image from 19.

Note that since total scapular and proximal humeral endoprosthetic reconstruction is a novel procedure, complication rates have been extrapolated from rates reported for reconstructions using modular spacers or proximal humeral endoprostheses cemented into the remaining humerus. 

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