Abstract
This study investigated whether a relationship exists between the length of the canthal–tragus line and the distance from the tragus at which the puncture point for arthroscope insertion should be made. On one side of 11 cadaver heads, a puncture point was marked 7 mm from the midtragus and 2 mm below the canthal–tragus line. On the other side, the distances were 10 mm and 2 mm, respectively. The arthroscope trocar and cannula were inserted at the marked points. The anatomical location of the arthroscope after insertion was confirmed by open dissection with the arthroscope in place. Following dissection, the canthal–tragus line was measured on each side of the cadaver’s head. For measurements >70 mm, puncture points 10 mm from the midtragus led to insertion of the arthroscope inside the upper joint compartment. For measurements ≤70 mm, puncture points 7 mm from the midtragus led to insertion of the arthroscope inside the upper joint compartment. This suggests that for canthal–tragus distances of >70 mm, the arthroscope should be inserted 10 mm from the midtragus and for distances ≤70 mm it should be inserted at 7 mm for the greatest likelihood of entering the upper joint compartment of the TMJ.
Arthroscopy of the temporomandibular joint (TMJ) is a minimally invasive surgical method of diagnosing and treating dysfunctions. Arthroscopic techniques have been modified for surgery of this joint, and arthroscopic instruments have been scaled down from those used for larger joints, to facilitate access and maneuverability .
The single puncture technique for TMJ arthroscopy described by H olmlund and H ellsing is the most widely used. They noted a line from the lateral canthus of the eye to the tip of the mid-portion of the ipsilateral tragus as a useful marker. They stated that the maximum concavity of the glenoid fossa lies 10 mm anterior to the midtragus point and 2 mm inferior to the tragus-canthus line. In another study they stated that the puncture point should be located 12 mm anterior to the tragus and 2 mm inferior to the tragocanthal line as this point is located between the temporal branch of the facial nerve and the superficial temporal vessels and is least likely to cause damage to these structures .
In their cadaver study, G reene et al used a different skin puncture point for arthroscopic surgery located 7 mm anterior to the posterior aspect of the tragus and 2 mm inferior to the canthal–tragus line.
The aim of this study was to investigate whether a relationship exists between the length of the canthal–tragus line and the distance from the tragus at which the puncture point for the insertion of the arthroscope should be made.
Materials and Methods
Studies were performed using a 2.3 mm 30 degree arthroscope with 2.8 mm cannula. (Stryker Co., San Jose, CA, USA). An assortment of operative instruments including scissors, scalpel blades, mucoperiosteal elevators, curved hemostats and retractors were used.
Operative procedures
11 adult cadavers (4 female and 7 male; 22 joints) were placed on the operating table in a dorsal–supine position with the cadaver’s head turned to expose the operative side. One puncture point was marked 7 mm from the midtragus and 2 mm below the canthal–tragus line on one side, on the other side a second puncture point was located 10 mm from the midtragus and 2 mm below the canthal–tragus line ( Fig. 1 ).
The head was turned away from the operator and as flat to the operating table as possible. The posterior mandible was distracted downward and forward to increase space for introduction of the arthroscope. The trocar and cannula of the arthroscope were inserted at the marked puncture points. The arthroscope was inserted perpendicular to the skin then directed anterosuperiorly towards the posterior slope of the eminentia. Every puncture attempt was made at the same angulation with both surgeons verifying the direction parallel to the external ear canal. No stab incision was used. Using a rotational motion, the trocar was punctured through the skin until the tip of the trocar contacted the lateral aspect of the zygomatic process of the temporal bone. The tip of the trocar was then used to dissect the periosteum covering this bone and, by moving the tip inferiorly, to pass this bony ledge so that the capsule was penetrated. Then the trocar and cannula were advanced to the proper depth.
The anatomical location of the arthroscope after insertion was determined by dissecting the TMJ while the arthroscope was still in place. An incision was made through the skin and subcutaneous tissue. A deeper dissection in the temporal region was carried out. When the condyle and its overlying temporomandibular ligament were reached, the flap was reflected inferiorly and anteriorly. The condyle was exposed and the anatomical position of the arthroscope recorded. The arthroscope was kept in its initial position throughout the dissection procedures ( Fig. 2 ). The arthroscope position was either inside the superior joint compartment (successful insertion) or anterior or posterior to the superior joint compartment (unsuccessful insertion).
After the dissection was completed, the canthal–tragus line was measured on each side of the cadaver’s head. All the measurements were performed by the same surgeon. The two surgeons alternated on which side of the cadaver’s head the trocar and cannula were inserted.
Since no patient identifiers were recorded, this study was exempt from IRB full review and did not require patient consent, consistent with Title 45 CFR Part 46, Subpart A, section b.4 ( http://www.hhs.gov/ohrp/humansubjects/guidance/45cfr46.htm#46.101 section b.4.).
Statistical analysis was performed using Fisher’s exact test. A p value of 0.05 or less was required for statistical significance.
Results
11 adult cadavers with 22 joints were used in this study. The cadavers were a random group made available to the authors without any screening system so that all sex, size and races were included. The mean canthal–tragus distance was 72 (65–83 mm). The mean depth of the arthroscope after insertion measured from the skin surface was 28.6 (range 25–30 mm) ( Table 1 ).
| Case No. | Sex | Operator | Canthal–tragus | Tragus-Puncture | Depth | Result |
|---|---|---|---|---|---|---|
| 1 | M | Operator 1 | 69 | 10 | 25 | Anterior to joint space |
| 2 | M | Operator 2 | 69 | 7 | 30 | Inside |
| 3 | M | Operator 1 | 66 | 7 | 30 | Inside |
| 4 | M | Operator 2 | 66 | 10 | 30 | Anterior to joint space |
| 5 | M | Operator 1 | 75 | 10 | 30 | Inside |
| 6 | M | Operator 2 | 75 | 7 | 30 | Posterior to joint space |
| 7 | M | Operator 2 | 70 | 10 | 30 | Anterior to joint space |
| 8 | M | Operator 1 | 70 | 7 | 30 | Inside |
| 9 | M | Operator 2 | 73 | 7 | 30 | Posterior to joint space |
| 10 | M | Operator 1 | 73 | 10 | 30 | Inside |
| 11 | M | Operator 2 | 74 | 7 | 30 | Posterior to joint space |
| 12 | M | Operator 1 | 74 | 10 | 25 | Inside |
| 13 | F | Operator 2 | 72 | 10 | 30 | Inside |
| 14 | F | Operator 1 | 72 | 7 | 30 | Posterior to joint space |
| 15 | F | Operator 2 | 74 | 7 | 30 | Posterior to joint space |
| 16 | F | Operator 1 | 74 | 10 | 27 | Inside |
| 17 | M | Operator 2 | 83 | 10 | 30 | Inside |
| 18 | M | Operator 1 | 83 | 7 | 20 | Posterior to joint space |
| 19 | F | Operator 2 | 71 | 10 | 25 | Inside |
| 20 | F | Operator 1 | 71 | 7 | 28 | Posterior to joint space |
| 21 | F | Operator 1 | 65 | 10 | 30 | Anterior to joint space |
| 22 | F | Operator 2 | 65 | 7 | 30 | Inside |
The data show that a trend exists in which the 70 mm canthal–tragus measurement is the critical point. That is, a puncture point located 10 mm from the midtragus and 2 mm below the canthal–tragus line led to greater success of insertion of the arthroscope inside the upper joint compartment than using the 7 mm puncture point when the canthal–tragus measurement was >70 mm. Conversely, when the canthal–tragus measurement was ≤70 mm, a puncture point located 7 mm from the midtragus and 2 mm below the canthal–tragus line led to greater success of insertion of the arthroscope inside the upper joint compartment than using the 10 mm puncture point. The two surgeons’ success rates for introducing the arthroscope showed no statistically significant difference ( Table 2 ).
| Operator 1 | Operator 2 | |
|---|---|---|
| Success | 6 | 5 |
| Failure | 5 | 6 |
The cadavers were divided into two groups: Group A (≤70 mm) contained four cadavers with 8 joints; and Group B (>70 mm) contained 7 cadavers with 14 joints. In Group A (≤70 mm), a puncture point located 7 mm from the midtragus and 2 mm below the canthal–tragus line led to insertion of the arthroscope inside the upper joint compartment in 100% of the insertions, while a puncture point located at 10 mm from the midtragus and 2 mm below the canthal–tragus line led to insertion of the arthroscope anterior to the upper joint compartment in 100% of the cases. The difference between the 7 mm and the 10 mm puncture points was significant (p < 0.05) ( Tables 3 and 4 ).
| Case No. | Sex | Operator | Canthal–tragus | Tragus-Puncture | Depth | Result |
|---|---|---|---|---|---|---|
| 21 | F | Operator 1 | 65 | 10 | 30 | Anterior to joint space |
| 22 | F | Operator 2 | 65 | 7 | 30 | Inside |
| 3 | M | Operator 1 | 66 | 7 | 30 | Inside |
| 4 | M | Operator 2 | 66 | 10 | 30 | Anterior to joint space |
| 1 | M | Operator 1 | 69 | 10 | 25 | Anterior to joint space |
| 2 | M | Operator 2 | 69 | 7 | 30 | Inside |
| 7 | M | Operator 2 | 70 | 10 | 30 | Anterior to joint space |
| 8 | M | Operator 1 | 70 | 7 | 30 | Inside |
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