The Research About Anatomy, Injury Diagnosis And Dynamic Biomechanics Of Medial Ankle Deltoid Ligament

Part ⅠThe anatomical research of medial ankle deltoid ligamentBackground and objectives:The deltoid ligament is the most important structure for the ankle stability. Currently, limited researches were available which explores its anatomical characteristics and a lot of controversial were still existed. The number of deltoid ligament anatomy studies was only one-sixteenth compared with the anterior cruciate ligament of the knee joint. The present study is aiming to observe and measure the deltoid ligament though specimen anatomy and analyze about its anatomical components, variations, origin and insertion sites and behaviors during ankle flexion motion.Materials and methods:Twenty below-knee specimens are included for the present study. All the specimens are fixed on a specific frame and the ankle medial approach is applied to expose the deltoid ligament. All ligament bands which comprised of the deltoid ligament are carefully distinguished and observed. Markers are then inserted into the bone to which each ligament bands are attached. The length, width and thickness of each band are obtained though the measurement on the standard X-ray films. The lengths of all bands are also measured at 5° interval during ankle flexion arc from 40°plantar-flexion to 20°dorsi-flexion. The motion ranges which a specific band is to be tight are also analyzed then. The angles between each bands and tibial longitudinal axis are also measured on the lateral x-ray film. The talus and medial malleolus are isolated and its ligament attachment sites are recorded by standard photography. The origin and insertion sites of each ligament are both qualitatively and quantitatively described.Result:The deltoid ligament in all specimens can be divided into the superficial and deep layer. Adipose tissue is found between the two layers in 6 specimens. No ligament fibers are found in the band which was referred as tibio-navicular ligament (TNL) previously. It is a thin soft tissue connected between anterior colliculus and dorsal aspect of talar neck and regarded as a reinforced structure of ankle capsule. The deltoid ligament is comprised of four bands which the tibiocalcaneal ligament (TCL) and the two ligaments in deep layer are constantly presented. The anterior border of TCL and posterior border of dATTL have the best Isometric behavior during ankle flexion motion. The ligament fibers anterior to the isometric borders are becoming tight at ankle plantarflexion while the fibers posterior to them are staut at dorsiflexion. All the deltoid ligament fibers are originated form anterior colliculus and inter-colliculus groove. No ligament attachment is found on the posterior colliculus. Attachment site of the superficial bands were on the medial half of the inferior surface while the all deep bands were on the lateral half. The origin of TSL was on the anterior half of anterior colliculus while the origin of TCL was on the posterior half. The TNL was originated from the intercollicular groove. For the deep bands, dATTL was originated from the most prominent process of anterior colliculus and the origin of dPTTL was exactly on an obvious triangle shaped fossa between the anterior and posterior colliculus. The photographs of the medial side of talus were taken and the coordinate system was established according to the described method.Conclusion:The deltoid ligament is comprised of four ligament bands. The most anterior part of deltoid ligament is regarded as reinforced structure of ankle capsule rather than the tibionavicular ligament. Reciprocal function between the ligaments is found for the deltoid ligament. No ligament is attached on the posterior colliculus and the accurate determination of ligament origin and insertion site is the basis of ligament reconstruction and biomechanics studies.Part II The diagnosis of partial deltoid ligament though external rotation stress test Background and objectives:The external rotation stress test has been the main approach for the diagnosis of deltoid ligament injuries. The recent clinical researches had revealed the existence of partial deltoid ligament. However, the results of stress radiographs in such cases are unavailable till now.Materials and methods:Sixteen fresh cadaveric specimens were included and randomly allocated into two groups. The ankle destabilizations were initiated with anterior portion of DL in the first group and posterior part of DL in the second one. All specimens were mounted in a fixture. Mortise views were taken after each destabilization stages when the ankles were placed at ankle maximal plantarflexion, neutral and dorsiflexion positions and stressed in standard external rotation force. The medial clear spaces were measured in all radiographs. The measurement results in intact ankle were regarded as baseline. The medial clear space values in each step were compared with the baseline. The statistical significant level was set as P<0.05.Results:The mean medical clear space in intact ankle was 2.60±0.39mm, 2.8±0.36mm and 2.45±0.26mm at maximal plantarflexion, neutral and maximal dorsiflexion positions. For the first group and when the ankles were placed at plantarflexion and neutral, significant differences of MCS were found after dissection of AiTFL (stage 3) and IM (stage 4). There was no significant difference of MCS at dorsiflexion for all stages of destabilization when compared with the baseline (P> 0.05). For the second group and when the ankles were placed at dorsiflexion and neutral, significant differences of MCS were also found after dissection of AiTFL (stage 3) and IM (stage 4). No significant difference of MCS at plantarflexion were detected for all stages of destabilization (P>0.05).Conclusion:The external rotation stress test could detect the partial deltoid ligament which combined with syndesmotic ligament ruptures. Ankle neutral position was recommended for diagnosis of partial DL ruptures under external rotation stress. Combinations of ankle dorsiflexion, neutral and plantarflexion during stress tests for a comprehensive assessment of deltoid ligament status still need to be further testified.Part III In-vivo dynamic length and tension variations of-deep deltoid ligament during the gait cycleBackground and objectives:The previous biomechanical studies concerning about deltoid ligament were mostly conducted during static or quasi-dynamic environments. The real biomechanical behavior of deltoid ligament could be hardly reflected though these in-vitro and static data. The present study is aiming to analyze the in-vivo length variation of deep deltoid ligament during gait cycle.Materials and methods:A healthy young male volunteer was selected for the test. The lower leg deformities and traumatic histories were excluded though comprehensive physical exam and x-rays. A CT scan was performed for the right ankle during its neutral position and non-weightbearing. All the CT images were imported into Mimics software and the three-dimensional models of talus and tibia was established. A complete gait cycle was collected though a fluoroscopy and nine key images during the gait were selected for the analysis. Images 1-4 were represent for the heel strike phase, images 5-7 were represent for the swing phase and the image 8-9 were stand for the toe off phase. The three-dimensional motion of talucrural joint during the gait cycle was obtained though the 3D-2D image matching technique. The bony attachment sites of deep deltoid ligament were determined with utilize of the anatomical results in the first part of the present studies. The in vivo deep deltoid ligament length variation was obtained though the distance change between the origin and insertion site.Results:Both the anterior and posterior deep deltoid ligament gradually shortened during heel strike phase and restored its length during swing phase. All deep ligaments achieved maximal lengths at toe off phase. The deep anterior tibiotalar ligament is in taut at early period of heel strike while no ligament was tight from intermediate period of heel strike to the late period of swing phase. All the deep deltoid ligaments were in taut status during the toe off phase.Conclusion:In the in vivo gait cycle motion, deep deltoid ligament was becoming tight during toe off phase. All the ligaments were slackened from intermediate period of heel strike to the late period of swing phase.