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Mini-incision shoulder arthroplasty
Despite patients’ eagerness to return to functional activities, standard postoperative rehabilitation programs must be followed.
Minimal disruption of soft tissue and the potential for faster recovery are attractive benefits of minimally invasive surgery. However, mini-incision surgery must meet the same standards and offer the same successful outcomes as traditional, larger-incision operations. And while mini-incision hip and knee replacements have become accepted, there are no reports on mini-incision shoulder arthroplasty.
The goals of mini-incision shoulder arthroplasty (MISA) are to decrease trauma to surrounding soft tissues, accelerate postoperative rehabilitation and decrease perioperative complications. However, if extensive releases of surrounding musculature are required, a minimally invasive approach may not be feasible. Careful patient selection is crucial at this stage in the development of this technique.
Currently, there are two techniques available to achieve the necessary exposure to perform MISA: (1) a concealed axillary incision and (2) a mini-deltopectoral incision. The choice of technique is based upon the pathology, the severity of disease, instrumentation and surgeon experience.
In this article, I discuss the indications, technique and complications of my preferred mini-deltopectoral approach to shoulder arthroplasty.
Indications
Glenohumeral arthritis: Many patients undergoing shoulder arthroplasty for arthritis have substantial contractures requiring extensive releases to expose and to properly address the pathology. The decision to perform MISA vs. traditional incisions must therefore be based on patient’s pathology, instrumentation available and surgeon experience. While MISA is becoming the more common approach in my practice, patients with large osteophytes and limited ranges of motion or large, muscular patients may require a traditional approach.
As in all cases of shoulder arthroplasty, preoperative anteroposterior (AP), lateral and axiallary radiographs are essential for preoperative planning and in deciding whether MISA is a reasonable approach (Figures 1, 2). Generally, in small women with satisfactory range of motion (FF of 100°; ER of 20°; IR to L3) and small osteophytes, a minimally invasive approach is reasonable. Decreased soft tissue disruption and limited subscapularis muscle detachment during surgery are beneficial for restoration of subscapularis function and accelerated postop rehabilitation.
Several reports have documented superior range of motion and better pain relief achieved in patients undergoing total shoulder replacement (TSR) vs. hemiarthroplasty for osteoarthritis. Therefore, the decision to perform hemiarthroplasty instead of TSR so that surgery may be done through an MISA approach is not recommended. Glenoid pathology in the setting of shoulder arthroplasty usually requires resurfacing with glenoid component. The decision to perform humeral head replacement (HHR) vs. TSR is made based on the pathology and not the approach to be used.
Four-part proximal humerus fractures: Hemiarthroplasty is indicated for treating four-part proximal humerus fractures with a nonsalvageable humeral head. A minimally invasive approach in HHR must provide adequate exposure for secure tuberosity fixation. It must also involve minimal soft tissue dissection to preserve the biological environment and foster bone healing. Advances in prosthetic designs aid surgeons in achieving these goals. These include a less bulky design to the proximal aspect of the prosthesis as well as coating the proximal aspect of the humerus with biologically compatible substances, such as tantalum.
Generally, the musculature around proximal humerus fractures is healthy and has excellent excursion, obviating the need for extensive surgical releases. Lack of stiffness combined with new technology for prosthesis placement and tuberosity fixation make the minimally invasive approach an excellent option for these patients.
Avascular necrosis: Several recent series have reported better results using total shoulder arthroplasty over hemiarthroplasty in patients with glenohumeral arthritis. But there are some cases where hemiarthroplasty is preferred. These include avascular necrosis (Cruess stages I-III, and sometimes IV) where the glenoid is not significantly involved. MISA is particularly useful in these patients, since glenoid exposure is not required.
Surgical technique
Positioning the arm to allow adequate visualization and instrumentation is critically important — especially in MISA. For this, we use a hydraulic arm positioner (TENET spider), which eliminates the need for another assistant and also avoids inevitable assistant fatigue from holding the arm throughout the procedure (Figure 3).
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Images: Blaine T |
Based on cadaveric studies and clinical experience, the author has found that the current instrumentation used for shoulder arthroplasty tends to exit the skin in a 5 cm arc centered and just lateral to the coracoid process (Figure 4). Furthermore, we and others have also found that the average diameter of the humeral head at the surgical neck is approximately 49 mm.
Based on these findings, the skin incision for shoulder arthroplasty must be at least 5 cm to allow placement of a humeral head component in shoulder arthroplasty. I therefore devised a skin incision that is centered just lateral to the coracoid process. This incision can be used in MISA for variety of diagnoses. The incision location allows better access to tuberosities in fracture cases and provides adequate glenoid exposure in arthritic disorders.
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The incision measures approximately 2 inches, just enough to deliver the humeral head from the wound. The placement of the starting incision is crucial for this approach. It has to be superior enough to provide direct access to the humeral canal for humeral preparation and placement of the prosthesis as well as adequate exposure of the glenoid.
The deltopectoral interval is identified and incised like traditional anterior approaches (Figure 5). Subcutaneous dissection is necessary along the deltopectoral interval superiorly and inferiorly for adequate exposure. Care is taken to protect the deltoid attachment to the clavicle and acromion. The cephalic vein is generally retracted with the deltoid muscle since there are more superiorly from the deltoid than inferiorly from the pectoralis. The pectoralis major is retracted medially, and the deltoid with the cephalic vein is retracted laterally.
The deltopectoral interval is developed and entered in a similar fashion. After exposure to the subscapularis muscle is achieved, the muscle is detached from the lesser tuberosity superiorly, starting at the rotator interval (Figure 6). The tendon is incised as laterally as possible, just medial to the bicep tendon. The rotator interval is also released all the way to the base of the coracoid.
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While in a traditional more generous incision, the role of biceps tenotomy is debated, MISA in most cases requires biceps tenotomy with or without later tenodesis to provide adequate visualization (Figure 7). The subscapularis is detached just enough to deliver the humeral head from the wound (Figure 8). Inferiorly, the subscapularis insertion may be preserved.
The humerus is prepared with tapered reamers which, with an incision based lateral to the coracoid, easily exit the skin (Figure 9). An intramedullary cutting guide is used to make the humeral neck cut. In MISA, this cutting guide must be low profile and should have the ability to be positioned outside the skin incision if necessary (Figure 10, 11). Humeral trials are then performed.
Correct component alignment is crucial as is adequate visualization; the incision should be enlarged if the visualization is poor. Before placing the final humeral prosthesis, bone tunnels are made and sutures are passed for future subscapularis repair. If total shoulder replacement is performed, attention is directed to the glenoid exposure (see below).
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Once the glenoid component has been replaced or if hemiarthroplasty alone is performed, humeral trials are placed to determine appropriate sizing (Figure 12). It is critical to place the humeral component in the appropriate version (usually 30° retroversion). Shoulder arthroplasty systems that allow version to be determined outside of the wound on the humeral inserters are critical for this step in MISA (Figure 13). Sutures are now placed in the humeral neck for later repair of the subscapularis per surgeon preference.
With the advent of new humeral prostheses that promote proximal bony ingrowth, uncemented humeral components are favored, particularly with the MISA technique (Figure 14). If cementation is performed, a cement restrictor is placed in the humeral canal to lie 2 cm distal to the tip of the prosthesis. To obviate problems with cement plug removal, I typically use an autograft bone plug fashioned from the resected humeral head. Cement is typically concentrated around the metaphyseal portion of the prosthesis, since it is primarily used to control humeral component rotation.
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Once the humeral component is fixed, trial head sizes are performed to reproduce the normal humeral head anatomy (Figure 15). This typically requires an offset humeral head component with the maximal offset in the posterosuperior location. Trial reduction is then performed. An appropriate head size will allow translation of the humeral head on the glenoid of approximately 50% of the glenoid surface in any direction. It is important to avoid overstuffing the glenohumeral joint, which can lead to persistent pain and postoperative stiffness. Once the appropriate head size is determined, the neck is dried with a clean sponge and the final humeral head is impacted on the morse taper (Figure 16).
Glenoid replacement in TSR
Glenoid exposure can be challenging even through the traditional incision. Therefore, careful patient selection for a minimally invasive approach for TSR is required. Proper glenoid preparation and component placement is crucial. After proper humeral preparation, as described above, a Fukuda retractor is placed to assess the glenoid (Figure 17). This helps retract the humerus lateral and posterior. An anterior spiked Darrach retractor (Figure 18) is then placed on the anterior rim of the glenoid. The provisional humeral stem is left in the canal during glenoid exposure and preparation, helping to protect the humeral stem integrity during retraction.
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To achieve adequate glenoid exposure, I perform capsular release superiorly, anteriorly and inferiorly around the glenoid. Care is taken to protect the axillary nerve by staying directly on the humeral neck inferiorly and retracting the inferior capsule in an inferior direction with a Darrach.
For routine TSR, where instability is not a problem and the rotator cuff is usually intact, an anterior capsulectomy may be performed to improve exposure. This should not proceed, however, below the 6 o’clock position (inferior glenoid) to avoid injury to the axillary nerve. A special spiked Darrach retractor is placed anteriorly for adequate visualization. In thin patients with good ranges of motion and minimal glenoid deformities, this is usually enough for adequate visualization and glenoid reaming, which is performed to achieve concentric stable component fit in appropriate version.
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Pegged or keeled glenoid components may be used. In one study, pegged glenoids were found to have superior fixation to keeled. However, the pegged component requires a larger glenoid vault and the keeled glenoid may be more appropriate in patients with a small native glenoid. Cement is pressurized in the pegged or keeled vault (Figure 19). Once we place the glenoid component, attention is turned back to the humerus. The humeral component and the humeral head are placed as described above.
After humeral component placement, we replace the upper part of the subscapularis securely to the lesser tuberosity at the normal anatomic subscapularis footprint. This step is critically important since subscapularis failure is the most common early complication of shoulder arthroplasty. The rotator interval is left open to prevent stiffness in external rotation. Wound closure of the wound is performed in the usual fashion with a running absorbable monofilament suture (Figure 20). Suture tails are left out of the wound and secured with steri-strips. Intraoperative AP radiographs are taken in all cases to verify size and prosthesis position before leaving the operating room.
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Postoperative care is critical for managing patients after MISA. Because of the smaller visible incision, patients believe that they have had less surgery and want to progress their therapy faster. Despite the patient’s eagerness to get back to functional activities, standard postoperative rehabilitation programs must be followed. The amount of time required for soft tissue healing is still the same regardless of the approach.
We reviewed the results of the first 12 consecutive patients treated with MISA by two surgeons (TAB and Louis U. Bigliani, LUB). Diagnoses included osteoarthritis (six patients), fracture (two patients), avascular necrosis (three patients), and cuff tear arthropathy (one patient). There were six HHRs and six TSRs.
One of two mini-incisions were used: either a 5-cm to 6-cm incision just lateral to the coracoid process, or a 7-cm to 8-cm concealed axillary incision below the coracoid process. The incision length averaged 6.2 cm (range 5 cm to 8 cm). A biceps tenotomy with tenodesis was performed in all patients where the biceps was present at surgery. At early (average 6 months) follow-up, no patient reported significant pain postoperatively.
There were two transient complications, including temporary musculocutaneous nerve palsy and postoperative wound drainage, both of which resolved without incident. One patient had a subscapularis rupture requiring repair. The musculocutaneous nerve palsy is believed to be related to excessive retraction required in the more medially based axillary incision. This incision has more recently been abandoned in favor of the incision lateral to the coracoid described in this article. Since using this incision, we have noted a high patient satisfaction level and our patients favor the final cosmesis from this incision (Figure 21).
Theodore Blaine, MD, is an assistant professor of orthopedic surgery at Columbia University and associate director of the Center for Shoulder, Elbow and Sports Medicine at the New York Orthopaedic Hospital, Columbia-Presbyterian Medical Center in New York.