BL-38 (Fu Xi) Superficial Cleft

What does BL-38 Fu Xi do?

BL-38 relaxes the sinews and alleviates pain, and clears heat and soothes contraction — a purely local record, entirely about tight and contracted tissue at the back of the knee.

• Relaxes the sinews and alleviates pain
• Clears heat and soothes contraction

The name trap, and it is the sharpest this library has found. “Fu Xi” is translated Superficial Cleft — the word xi, cleft, sitting right there in both the pinyin and the translation. BL-38 is not the Bladder channel’s Xi-Cleft point. Querying our own category records, the twelve regular-channel Xi-Cleft points are LU-06, LI-07, ST-34, SP-08, HT-06, SI-06, BL-63, KI-05, P-04, SJ-07, GB-36 and LIV-06 — the Bladder’s is BL-63 Jin Men, on the foot. (Four more belong to the extraordinary vessels — BL-59, KI-08, GB-35, KI-09 — making sixteen in all, and our data holds every one. BL-38 is not among any of them.) The xi in this name means simply a crevice or hollow, describing the depression at the back of the knee.

That makes four name traps documented in this channel and its neighbours, all verified by query rather than assumed: BL-07 (tian, not a Window of Heaven point), BL-08 (luo, not a Luo-Connecting point), DU-02, DU-05 and DU-07 (shu, not Back-Shu points), and now BL-38 (xi, not a Xi-Cleft point). A point name is a description, not a classification, and this channel is where that distinction matters most.

Why sinews and contraction, at this point. BL-38 sits beside the hamstring tendons where they cross the back of the knee — the place where tight tissue is most palpable in this region. Its indications name the popliteal tendons directly, and GB-34 Yang Ling Quan, the Hui-Meeting point for the sinews, sits just below the knee on the other side.

Source: Sacred Lotus sources & references (channel, action, location and translation records; all twelve Xi-Cleft points queried and BL-38 confirmed NOT among them; the BL-07, BL-08, DU-02, DU-05, DU-07 and GB-34 records checked against our own data), cross-referenced against multiple online sources.

What is BL-38 Fu Xi used for?

BL-38 is used for numbness of the buttock and thigh, and for contracture of the tendons behind the knee. Our own indication record is reproduced here in full — two entries, one of the shortest lists in the library.

• Numbness of the gluteal and femoral regions
• Contracture of the tendons in the popliteal fossa

Two entries, and the page will not pretend otherwise. BL-38 is a narrowly specified local point in our source material: tight tendons behind the knee, and numbness in the territory above. It records no organ action, no systemic indication, nothing beyond the region. Where a record is this short, this library states its limits plainly rather than filling the space — the same treatment given to BL-06 in the scalp run and DU-07 on the spine.

Note the direction the numbness runs. The indication is numbness of the buttock and thigh — the region above the point, not below it. That is unusual: most limb points record symptoms distal to themselves or along the whole channel. It is consistent with the classical view of this region as where the channel’s course through the thigh terminates.

An honest note. Numbness in the buttock or thigh requires medical assessment — particularly if it is new, spreading, or accompanied by weakness. Numbness in the saddle region, weakness in both legs, or any change in bladder or bowel control is a medical emergency requiring immediate care. This record documents classical use and should not delay that.

How it is combined. With BL-39 Wei Yang one cun below and BL-40 Wei Zhong in the centre of the same crease. With BL-37 Yin Men up the thigh. With GB-34 Yang Ling Quan, the influential point for the sinews, for the contracture indication. All held here.

Source: Sacred Lotus sources & references (indication record; the BL-06, BL-37, BL-39, BL-40, DU-07 and GB-34 records queried and compared from our own data), cross-referenced against multiple online sources.

Where is BL-38 Fu Xi located?

BL-38 is at the back of the knee, one cun above BL-39, on the INNER side of the biceps femoris tendon — the prominent cord you can feel on the outer edge of the hollow behind the knee.

• 1 cun superior to BL-39 Wei Yang
• On the medial side of the tendon of biceps femoris — the outer hamstring tendon
• BL-40 Wei Zhong sits at the midpoint of the crease behind the knee

The tendon is an excellent landmark, and the side of it matters. Biceps femoris stands out clearly when the knee is bent against resistance, and our record specifies the medial side — the side toward the middle of the knee. That is not a detail to skim: the lateral side of the same tendon is a different position with different structures beneath it, and “beside the biceps femoris tendon” without the side is an ambiguous instruction.

Where this point sits in a tight cluster. BL-38, BL-39 and BL-40 all lie within about an inch of one another at the back of the knee, and each has a different role — BL-40 being the He-Sea point and one of the most-used points on the channel. As on the fifth metatarsal and at the Pericardium wrist, crowding means that mistaking one for a neighbour substitutes a category.

On the name. “Fu Xi” — Superficial Cleft. The cleft is the hollow behind the knee; fu, superficial or floating, distinguishes it from deeper structures. Positional — and, as set out above, not a Xi-Cleft designation.

Source: Sacred Lotus sources & references (location and translation records, retained unchanged including the medial-side specification; the BL-39 and BL-40 positions and the twelve Xi-Cleft records queried from our own data).

• A Manual of Acupuncture (p. 297): On the back of the knee, 1 cun superior to Weiyang BL-39, on the medial side of the tendon of biceps femoris.
• Chinese Acupuncture and Moxibustion (p. 183-184): 1 cun above Weiyang (BL-39) on the medial side of the tendon m. biceps femoris. The point is located with the knee slightly flexed.

How is BL-38 Fu Xi needled?

Our own record states perpendicular insertion of 0.5–1.0 inch, with moxibustion applicable — and the structure that matters here is the COMMON FIBULAR NERVE, which runs along the medial border of the very tendon our record uses as the landmark. What follows is a neutral record of what the reference literature documents. It is not instruction, and this page does not teach technique.

• Angle and depth as recorded: perpendicular, 0.5–1.0 inch — notably shallower than the 1.0–2.0 inches recorded at BL-37 up the thigh, because the tissue thins as the leg narrows toward the knee.
• Moxibustion: recorded as applicable.
• Regional anatomy: the biceps femoris tendon forms the upper lateral border of the popliteal fossa; the common fibular (peroneal) nerve descends along its medial border to pass around the neck of the fibula, where it is superficial and vulnerable; the popliteal vessels and the tibial nerve lie deeper and more medially within the fossa.

The landmark and the structure are the same feature, and this library has a name for that pattern. Our record locates BL-38 by the medial border of the biceps femoris tendon; the common fibular nerve runs along that same border. It is the same relationship documented at ST-42, where the dorsalis pedis pulse is both how the point is found and what the record warns about, and at LU-08 with the radial artery. Unlike those two, our own BL-38 record carries no explicit caution — and this page does not invent one. The anatomy is stated because it is true; the absence of a recorded warning is stated because that is what our data holds.

Hazard, stated proportionately. No body cavity, no pleura, no great vessel at this position — the popliteal artery and vein lie deeper and more medially, within the fossa proper rather than at its upper lateral border. The relevant structure is a superficial nerve.

What is not claimed. No study measuring a safe depth at BL-38 could be located, and none is borrowed. The paediatric CT study this library uses covers 23 points on the trunk and shoulder and does not reach the knee. No case report naming BL-38 was located, and none is asserted.

Source: Sacred Lotus sources & references (needling record, retained unchanged, and BL-37's recorded depth compared; the ST-42 and LU-08 arterial-caution records queried and attributed to those points; the point list of PMID 26922245 / PMC4769822 confirmed not to include BL-38), cross-referenced against multiple online sources; regional anatomy from standard anatomical description.

Is there research on BL-38, and what should a reader know?

No trial isolates BL-38. Where the point appears it is one component of a knee or leg protocol, and a study that includes a point in a protocol is not evidence about that point. It is also one of the less-used points on the channel, so it appears in fewer protocols than its neighbours.

The neighbouring point with the literature is BL-40 Wei Zhong, an inch away, which is among the most-used points on the Bladder channel and appears in most low-back protocols. Evidence about BL-40 is evidence about BL-40. The short distance makes that worth stating explicitly, exactly as our P-04 and P-07 records do about P-06.

What this page can state with confidence, including its limits. BL-38 records two indications only — numbness of the buttock and thigh, and contracture of the tendons behind the knee — and no organ or systemic action. It is located on the medial side of the biceps femoris tendon, a side-specific instruction our record gives and a reader should not drop. The common fibular nerve runs along that same border. And despite xi appearing in both its name and its translation, it is not a Xi-Cleft point — that is BL-63, verified against the full set of sixteen.

A note on searching for it. “BL 38”, “UB 38” and “Fuxi” searches return protocol trials and a great deal of unrelated material — Fuxi is a major figure in Chinese mythology and a very common name in publications, place names and institutions, which makes it one of the poorest search terms in the whole point system. Our library codes this channel BL- while some sources use UB-. Any claim attached to this point should be checked against what a study actually used.

Source: Sacred Lotus sources & references (action, indication, location and needling records; the twelve Xi-Cleft points and the BL-39 and BL-40 records queried and verified against our own data).