A Concise and Comprehensive Description of Shoulder Pathology and Procedures: The 4D Code System

Background. We introduce a novel description system of shoulder pathoanatomy. Its goal is to provide a comprehensive three-dimensional picture, with an additional component of time; thus, we call it the 4D code. Methods. Each line of the code starts with right versus left and a time designation. The pillar components are recorded regardless of pathology; they include subscapularis, long head of biceps tendon, supraspinatus, infraspinatus, and teres minor. Secondary elements can be added if there is observed pathology, including acromioclavicular joint, glenohumeral joint, labrum, tear configuration, location and extent of partial cuff tear, calcific tendonitis, fatty infiltration, and neuropathy. Results. We provide two illustrative examples of patients which show the ease and effectiveness of the 4D code. With a few simple lines, significant amount of information about patients' pathology, surgery, and recovery can be easily conveyed. Discussion. We utilize existing validated classification systems for parts of the shoulder and provide a frame work to build a comprehensive picture. The alphanumeric code provides a simple language that is universally understood. The 4D code is concise yet complete. It seeks to improve efficiency and accuracy of the communication, documentation, and visualization of shoulder pathology within individual practices and between providers.


Introduction
There are numerous classification systems in the literature that define various pathologic findings associated with the shoulder [1][2][3][4][5][6][7][8]. Individually each of these classifications is accurate and useful in describing a specific portion of the shoulder anatomy or pathoanatomy. Currently, no description system exists to convey a comprehensive threedimensional image of the shoulder in a concise and reproducible format. In this paper, we introduce a description system to fill this void. The 4D code, as we call it, incorporates a complete three-dimensional picture of the shoulder with the additional component of time. It seeks to improve efficiency and accuracy of the communication, documentation, and visualization of shoulder pathology within individual practices and between treating surgeons.
As the knowledge and ability of a specialty expand and improves, it is a natural progression that the classification systems utilized by the profession must evolve. Historically, the rotator cuff was visualized as a single pathologic entity, and classification systems described them as such [9]. These prior systems were sufficient for the knowledge of that era. With time, our understanding of shoulder anatomy and physiology has evolved. The rotator cuff is comprised of structurally and functionally distinct components which work synergistically to achieve full function of the shoulder. Goutallier exposed the importance of the status of the muscle, and implications of fatty infiltration when evaluating and treating rotator cuff disorders [10,11]. Warner has made us aware of the role the suprascapular nerve in the function of the rotator cuff and its causal relationship to various shoulder problems [12,13]. This expansion of knowledge  requires a parallel improvement and update in the method of classification utilized. In addition to the rotator cuff, other structures need to be considered simultaneously in order to fully achieve a global view of the shoulder, including the acromioclavicular (AC) joint, the glenohumeral joint, the long head of biceps tendon, the labrum, and associated nerves. Each of these structures and their interactions directly affect the ultimate integrity and performance of the shoulder complex as a whole.
Classification systems for tears of the rotator cuff tendon have been proposed based upon specific characteristics such as size of the lesion, number of tendons involved, and the reparability of the tear [1-8, 14, 15]. In addition to these broader-based classifications, specific classification systems focusing on individual tendons have also been proposed. Patte developed a classification for lesions of the supraspinatus, infraspinatus and teres minor, Lafosse for tears of the subscapularis, and Curtis and Ellman for partial rotator cuff tears [2,4,7].
Individually, these rotator cuff tear classification systems do provide information about the condition of the patient's shoulder, but are limited in their description of the shoulder as a whole. In addition, none of these systems provides any information about the status of the associated joints, ligaments, tendons, and nerves; their concomitant assessment and treatment are important in optimizing patients' outcome. The limitations of these current classification systems mandate the development of a new, concise, and expandable classification system that covers all rotator cuff tendon pathology, and is inclusive of the surrounding structures of the shoulder. The 4D code was developed with these explicit goals.

Methods
The aim of the 4D code is to provide a logical method of describing shoulder pathology using universal numbers and letters. The 4D code seeks to provide a complete description of the shoulder in a concise format, without sacrificing detail, and allows a practitioner to glean the pertinent information in regards to preoperative, operative, and postoperative condition of the shoulder. This allows the appropriate treatment protocols to be adjusted and optimized for each individual patient in an efficient and comprehensive manner.
The 4D code is one or multiple lines of alpha-numeric text, each line denoting the condition of the shoulder at one point in time. We introduce our methodology by dividing the 4D code into its fundamental elements and secondary elements.

The Fundamental Elements.
The fundamental elements of the 4D code start with the shoulder sidedness and the time code. Next are the pillar components ( Figure 1). These represent anatomical structures of the shoulder which serve as important scaffolds for the 4D code. Starting from the anterior aspect of the shoulder and moving posteriorly, the pillar components include: subscapularis, long head of biceps tendon, supraspinatus, infraspinatus, and teres minor. These structures form the foundation of the shoulder and are always described, regardless whether they have pathology or not. The pillar components have the greatest influence on symptoms, surgical decisions, and patient's function.
An example of the 4D code which includes the fundamental elements is shown in Figure 2. We will discuss Advances in Orthopedics  Partial tear of superior third 2 Complete tear of superior third 3 Complete tear of superior two-thirds 4 Complete tear, head concentric, fatty infiltration 1-3 5 Complete tear, head eccentric, fatty infiltration > 3 2.1.1. Sidedness. The first letter is the sidedness of the shoulder. An "R" or "L" will start all lines of 4D code, so there is consistency in the reporting of the shoulder of interest of a given patient.

Time Code.
The second fundamental element is the time code ( Figure 3). This allows the pathology of the shoulder to be correlated to a specific time in the treatment time-line.
(i) D− -before surgery: the code that follows is the condition of the shoulder based on history, examination, radiological, and other studies.
(ii) D-day of surgery, prior to any repair: this includes the important information gathered from diagnostic arthroscopy. The code may be different from before surgery (time D−) due to evolution or clarification of pathology.
(iii) D+ -end of surgery: this presents the condition of the shoulder once repair is complete.
(iv) D+ time-a certain time after surgery: D+6W would represent the time point of 6 weeks postoperatively. M (months) and Y (years) can also be used.

Subscapularis.
The first of the pillar components describes the condition of the subscapularis tendon. We use the Lafosse classification system, which is based on tear size and location, humeral head concentricity, and degree of fatty infiltration (Table 1) [4].

Long
Head of Biceps Tendon. The 4D code documents the condition of the long head of biceps tendon into the following categories: (i) BN-normal; (ii) BP-pathological; (iii) BA-absent or tenotomized; (iv) BT-tenodesed.

Supraspinatus, Infraspinatus, and Teres Minor.
To assess the tear in the coronal plane, the Patte classification system is used to describe the supraspinatus, infraspinatus, and teres minor tendons ( Figure 4) [7]. Stage 1 describes a tear with minimal retraction; stage 2 describes retraction to center of humeral head; stage 3 describes retraction to glenoid. A "0" is assigned for normal tendons.
Putting the fundamental elements of the 4D code together, the example in Figure 2 (RD 2 BP 2 1 0) describes the condition of a right shoulder after surgical examination but prior to any intervention. The shoulder has a complete lesion of the superior third of subscapularis (Type 2). The long head of biceps tendon is pathological (BP). Supraspinatus tendon is torn and retracted to top of humeral head (stage 2). Infraspinatus tendon is torn with minimal retraction (stage 1). Teres minor tendon is normal.

The Secondary Elements.
The secondary elements expand the descriptive capability of the 4D code system. They add to the shoulder sidedness, time code, and the pillar components. Unlike the fundamental elements which appear with every line of 4D code, the secondary elements are documented only if there is pathology. These structures and conditions include: the acromioclavicular (AC) joint arthritis, glenohumeral joint arthritis, labral pathology, fatty infiltration, and any associated nerve pathology. Additional description of a rotator cuff tear may be added, including shape of a tear, bursal-versus articular-sided, and presence of calcific tendonitis. Figure 5 shows an illustrative line of 4D code which includes all of the secondary elements.

Acromioclavicular Joint.
If there is presence of AC joint disease, this can be added to the 4D code as a secondary element. We choose to place the following code immediately after the time designation: (i) AC-presence of AC joint arthritis; (ii) ACR-status post AC joint resection.

Glenohumeral Arthritis.
The presence of glenohumeral osteoarthritis is documented using the Samilson classification [8]; it is based on the size of the inferior humeral head   osteophyte (Table 2). In the 4D code, we use "GH" followed by the Samilson stage to denote glenohumeral arthritis; this is placed before the subscapularis code.

Labrum.
With superior labral pathology, we use Snyder's classification [16] of the superior labrum anterior posterior (SLAP) tears, later expanded by Maffet et al. [17] ( Table 3). The remainder of the labrum can be document using the nomenclature of a clock face. In the 4D code, the following designations are used for labral pathology, placed in the code between subscapularis and biceps tendon: (i) SLx: type x SLAP lesion; (ii) SLD: debridement of SLAP lesion; (iii) SLR: SLAP repair; (iv) Lx-y: labral detachment from x to y o'clock, for example, L2-6 is a Bankart lesion from 2 to 6 o'clock; (v) LD: labral debridement; (vi) LR: labral repair.

Tear Configuration.
The shape of the rotator cuff tear can be incorporated into the 4D code. Full thickness tears have been described as U-shaped, V-shaped, or L-shaped in the literature. We use the following designation immediately before the tendon it is associated with: (i) U: U-shaped tear; (ii) V: V-shaped tear; (iii) AL: anterior L-shaped tear; anterior corner detachment; (iv) PL: posterior L-shaped tear; posterior corner detachment.  Degenerative, frayed superior labrum with intact biceps anchor. 2 Biceps anchor detachment from the superior glenoid tubercle. 3 Bucket-handle tear of the labrum with an intact biceps anchor. 4

Partial Thickness
Bucket-handle tear of the labrum that extends into the biceps tendon. 5 Anterior-inferior Bankart that extends superiorly to include an unstable biceps anchor 6 Unstable flap tear of the labrum with a detached biceps anchor. 7 Superior labral detachment with extension into the middle glenohumeral ligament. Partial tear > 6 mm deep Fatty streaks 2 Significant fat, but more muscle than fat 3 Equal amount of muscle to fat 4 Fat is greater than muscle 2.2.6. Calcific Tendonitis. Calcium deposit in the rotator cuff tendon can cause exquisite pain and is an important pathology in the shoulder. If calcific tendonitis is present, the letter C can be placed in the 4D code for the particular tendon involved.

Fatty Infiltration of Rotator Cuff.
The presence of fatty infiltration in the rotator cuff muscle provides additional information regarding chronicity of the tears and has significant impact on surgical decision making and the potential for return of function [11]. Fatty infiltration is documented in the 4D code according to the Goutallier classification (Table 5) [10]. This component being a secondary element, it is documented only if there is presence of fatty infiltration. A letter "G" is placed after the pillar components and is followed by four numbers, corresponding to fatty infiltration of subscapularis, supraspinatus, infraspinatus, and teres minor, respectively.

Nerve Pathology.
If any neuropathy is present around the shoulder based on history, examination, imaging, and neurodiagnostic studies, this can be designated in the 4D code: (i) SSN-suprascapular nerve injury; (ii) SSNR-status post suprascapular nerve release; (iii) AXN-axillary nerve injury; (iv) LTN-long thoracic nerve injury. Table 6 summarizes the fundamental and secondary elements of the 4D code, including its possible codes and corresponding descriptions.

Results
We present two patients from our practice as illustrative examples of the utility of the 4D code.

Patient 1.
A 64-year-old lady initially presented in consultation with right shoulder pain. Her symptoms had started insidiously one year earlier. She did not improve with nonoperative treatments and elected to undergo rotator cuff repair. She did well initially; however, she sustained a fall 2 years after surgery and has returned to the office. Using the 4D code, her clinical picture can be summarized as follows. From these five lines of code, a significant amount of information is conveyed. Line 1 portrays the condition of the right shoulder at time of consultation (D−). Based on examination and three-dimensional imaging, there is partial tear of the upper subscapularis tendon, biceps tendon is diseased, and supraspinatus tendon is torn and retracted to the level of humeral head. Line 2 shows the condition of the shoulder on the day of surgery after diagnostic arthroscopy (time D); superior subscapularis tendon is noted to be completely torn, and in addition to supraspinatus tear, infraspinatus is torn as well without retraction. In line 3, we see the extent of the surgical interventions (time D+), which include tenodesis of the long head of biceps, successful anatomical repair of all rotator cuff tendons, and release of the suprascapular nerve. At the six-week-followup (time D+6W), line 4 shows that the repair is intact. After patient sustained a fall two years later (time D+2Y), examination and additional imaging shows (line 5) that the cuff repair remains intact, but there is a bursal-sided partial tear of the supraspinatus tendon.
No additional secondary elements are listed because this patient had no AC joint or glenohumeral joint arthritis, labrum was normal, and there is no fatty infiltration of the rotator cuff muscles.

Patient 2.
This patient is a 58-year-old male with a long history of dominant right shoulder pain and functional limitation. At the patient's initial visit, he complained one year of worsening right shoulder pain, atraumatic in onset.
He had failed to improve despite physical therapy and one subacromial corticosteroid injection. His examination showed a torn subscapularis tendon from positive Liftoff and Bear-hug tests. He also had weakness of the supraspinatus and infraspinatus muscles. He had bicipital groove pain but no AC joint tenderness. His CT arthrogram confirmed and added to the exam findings ( Figure 6). There was complete tear of the upper portion of subscapularis, diseased/subluxed biceps tendon, and moderately retracted supraspinatus and infraspinatus tendons. No obvious fatty infiltration was visualized. Based on these information, we recorded the following 4D code. Line 1: RD− 2 BP 2 2 0. The patient was indicated for surgery, and photographic documentation was done during diagnostic portion of the arthroscopy (Figure 7). It confirmed initial findings with the exception that the subscapularis tear was more significant, affecting the upper two-thirds of the tendon attachment, making it a Lafosse type 3 tear. The second line of this patient's 4D code reflected the changes.
Line 2: RD 3 BP 2 2 0. The pathology was addressed with an anatomic, arthroscopic repair of the rotator cuff, and arthroscopic proximal biceps tenodesis. Final pictures are shown in Figure 8. Line 3 documented the status of the shoulder at the conclusion of the surgical intervention.
Line 3: RD+ 0 BT 0 0 0. The patient has done well postoperatively. At his 3-year-followup, he complained of minimal pain. His constant score was 90, with full, symmetric ranges of motion, but mild weakness in the right supraspinatus muscle. He also showed mild tenderness at the AC joint. CT arthrogram was obtained (Figure 9), which showed re-tear of supraspinatus (without retraction), and articular-sided partial tear of infraspinatus. There is also evidence of AC joint arthritis. Line 4 reflects these changes at the 3-year mark. The patient was very satisfied with the final result and no further intervention was indicated.

Discussion
An exponential increase in the knowledge of pathologic conditions affecting the shoulder has allowed us to define the natural history of various disease processes. Similarly, surgical techniques have evolved to address the uniqueness of each element of the rotator cuff and surrounding structures. The expansion of knowledge and improvement of techniques (c) Inferiorly, the upper two-thirds of the lesser tuberosity is exposed after debridement. There is significant fraying of the dislocated biceps tendon on the right-hand side. There is also the "comma sign" from the medially retracted anterior-superior rotator cuff tear. (d) This is the articular view of the grade 2 supraspinatus tear retracted to level of the humeral head. (e) This is a lateral view of the exposed humeral head with the grade 2 infraspinatus tear. (f) Infraspinatus tendon has delaminated into two layers. is internationally understood. By consolidating previously validated schemes, the basic tenets of an effective classification system-simplicity, accuracy, and applicability-are maintained.
The premise of utilizing such a code to create a threedimensional image is derived from the same concept of the binary code that computers use to perform their necessary functions. Just as a computer can process a picture from a combination of 0's and 1's, we have established a systematic grouping of letters and numbers to allow the human mind to formulate a complete picture of the shoulder. Additionally, to our knowledge, this is the first description system in the literature that incorporates the dimension of time, which is a progressive and necessary step forward.
Its reproducibility and simplicity permit communication between physicians, therapists, and other members of the care team. Its flexibility and adaptability should have wide appeal. Our experience with the 4D code thus far has shown providers of all levels have been able to easily learn, apply, and clearly communicate with the system. Ultimately, it is a significant step forward in how shoulder pathology is evaluated, documented, and discussed.

Conclusion
The 4D code is developed to provide a concise yet comprehensive view of the shoulder pathoanatomy. It provides a three-dimensional picture and incorporates the element of time. It consolidates previously validated classification and grading systems into lines of alpha-numeric text that is easily conveyed. Its simplicity and completeness aid patient care between members of a care team as well as communication between surgeons internationally. We think the wider adoption of the 4D code can be a large step forward in the documentation of shoulder pathology and the exchange of this information.